Tonight’s sky of new research

CHEX-MATE: Density profile reconstruction in galaxy clusters

I. Bartalucci, G. W. Pratt, E. Rasia+26 more

AstronomerWithin the CHEX-MATE framework, this simulation study tests how morphology, dynamical state, and methodological choices affect reconstruction of intracluster gas radial density profiles. For 109 simulated clusters analysed along 40 independent lines of sight, azimuthal median-based deprojection recovers the true density with negligible bias over 0.15–1.3 R500. Mean-based profiles are sensitive to substructure: accurate masking can reduce bias below 5%, but discrepancies increase substantially in disturbed systems or when substructures remain unresolved. The mean-to-median density ratio statistically traces projected gas inhomogeneities, with intrinsic scatter and projection limiting its usefulness for individual clusters. The authors therefore favour complementary mean and median profiles for large X-ray cluster samples.

PublicUsing 109 simulated galaxy clusters viewed from 40 independent directions, researchers tested ways to reconstruct how gas density changes with distance from a cluster’s centre. A method based on the median, or middle value, recovered the simulated gas density with negligible systematic error over the tested radial range. A method based on the average was more sensitive to gas clumps. Carefully excluding those clumps reduced its systematic error to below 5%, but larger discrepancies remained in disturbed clusters or when clumps could not be resolved. Comparing the two methods can reveal gas unevenness statistically, although viewing direction and cluster-to-cluster variation limit what it tells us about any one cluster. The study recommends using both methods together for large X-ray cluster samples.

Young explorerGalaxy clusters are big groups of galaxies with gas between them. Scientists used computer-made clusters to test two ways of finding how thick the gas is in different parts. Picking the middle value worked very well in the region they tested. Taking an average was more easily thrown off by lumps of gas, especially when the lumps could not be picked out. Comparing both ways can help scientists learn how lumpy the gas is, but it cannot tell the whole story for every cluster.

Gravitational waves flooding the Universe after wall domination

Sabir Ramazanov, Zhen-Min Zeng

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThe authors explore a possible early-Universe scenario in which domain walls temporarily dominate the energy density, interrupting radiation domination before annihilating into particles. During wall domination, expansion accelerates while the network's comoving correlation length remains constant. Tensor modes sourced by the network freeze upon horizon exit, analogously to inflationary fluctuations, and contribute to a gravitational-wave background after re-entering during the subsequent radiation era. The predicted spectrum differs markedly from that of walls that remain subdominant until annihilation. The authors predict signals accessible to present-day and future facilities over a broad frequency range, and a potentially significant contribution to the effective number of neutrino species unless the duration of wall domination is sufficiently constrained. These are predictions of a proposed scenario, not reported detections.

PublicThe paper explores a possible episode in the early Universe when structures called domain walls briefly became its dominant component, causing its expansion to accelerate before the walls disappeared into particles. In this proposal, the walls generate gravitational waves that later form a background of ripples in spacetime. The predicted pattern of these waves differs substantially from what would be expected if the walls never became dominant. The authors predict that the waves could be detectable by current and future facilities across a wide range of frequencies. Their energy could also significantly affect the effective number of neutrino species, a measure of the Universe's radiation content, unless the wall-dominated episode was limited in duration. The abstract reports theoretical predictions, not observations of these waves.

Young explorerThe scientists imagine that, long ago, the Universe might have had things called domain walls. For a while, these walls could have made space grow faster and faster before turning into tiny particles. They could also have made ripples in space, like ripples on water. The scientists predict that tools we have now or build later could spot these ripples. If the walls were in charge for too long, the ripples could carry enough energy to make an important difference to the Universe. This is an idea about what might have happened, not something the scientists say they have seen.

An obstruction to cosmic acceleration from shift-symmetric dark sector interactions

Jose Beltrán Jiménez, Luis J. Garay, Erik Jensko+1 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis theoretical study uses the effective field theory of cosmological media to examine derivative interactions between a perfect fluid and a superfluid in the dark sector. Within this framework, these interactions cannot support slow-roll expansion while remaining free of instabilities. When the medium is decomposed into effective dark matter and dark energy components, stability conditions also exclude a phantom-to-non-phantom crossing. These constraints provide guidance for constructing theoretically viable dark sector models; they are not observational findings.

PublicResearchers used a mathematical framework to study models in which the universe’s dark sector consists of two interacting kinds of fluid. They find that the interactions studied cannot sustain a slowly changing expansion without instabilities. Treating the same medium as effective dark matter and dark energy also rules out a particular transition in dark energy’s behavior, called a phantom-to-non-phantom crossing. These are theoretical limits on this class of models, not measurements of how the universe actually behaves.

Young explorerScientists used math to imagine the universe’s mysterious dark ingredients as two kinds of fluid working together. In their model, the fluids cannot make space grow in a certain slowly changing way without becoming unstable. This helps scientists decide which ideas could work. It is a lesson from a model, not something they saw in the sky.

PrimordialPy: A Python library for single-field inflation, primordial black holes, and scalar-induced gravitational waves

Flavio Pineda

AstronomerPrimordialPy is an open-source Python package for computing predictions of arbitrary canonical single-field inflationary models specified through V(φ) and its parameters. It numerically solves the background dynamics and curvature perturbation equation to evaluate primordial scalar and tensor power spectra across relevant scales, then computes the resulting primordial black hole mass fraction and abundance and the associated scalar-induced gravitational-wave spectrum. The authors describe a modular, efficient, accessible design with documentation, validation benchmarks, and examples. These are model-dependent theoretical calculations, not observational detections of primordial black holes or gravitational waves.

PublicThe authors introduce PrimordialPy, a free, open-source Python toolkit for exploring theories of inflation in the early universe. Users supply a model, and the software calculates its predicted primordial fluctuations, the resulting abundance of primordial black holes, and an associated gravitational-wave signal. It supports a particular class of inflation theories driven by a single field, rather than every possible theory. Documentation, validation benchmarks, and examples accompany the package. The work presents a calculation tool, not evidence that these black holes or gravitational-wave signals have been observed.

Young explorerPrimordialPy is a computer toolbox for exploring ideas about the universe when it was very young. Scientists give it a model, and it works out what tiny changes, black holes, and ripples in space that model predicts. It comes with instructions and examples. It helps scientists calculate what might happen; it does not mean they have found those black holes or ripples.

Observational Test of the Maximum-Entropy Conjecture for Black-Hole Mergers with GW250114

Yang Jiang, Qing-Guo Huang

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis study tests the conjecture that a binary black-hole merger selects the Kerr remnant with maximum Bekenstein-Hawking entropy, subject to post-Newtonian or energy and angular-momentum balance constraints. For GW250114, the authors infer progenitor and remnant properties separately from pre-merger and post-merger signals, construct a surrogate Kerr entropy along the inferred energy-angular-momentum trajectory, and compare its maximum with independent ringdown estimates. The conjecture predicts a remnant mass of 70.0 (+0.35/-0.21) solar masses and dimensionless spin of 0.70 (+0.00/-0.01), versus ringdown estimates of 72.3 (+3.6/-3.7) solar masses and 0.74 (+0.05/-0.07). The entropy deviation is consistent with zero within the fiducial analysis's 68% credible interval. Variations in pre-merger truncation time and quasi-normal-mode content reveal no compelling discrepancy, supporting compatibility for this event rather than establishing the conjecture.

PublicWhen two black holes merge, what determines the mass and spin of the black hole left behind? This study tests a proposed rule: the final black hole has the largest possible entropy, a quantity used to describe black holes, within constraints on energy and angular momentum. Using the gravitational-wave event GW250114, the researchers analyzed the signals before and after the merger separately. The rule predicts a final mass of about 70 times the Sun's mass and a spin close to the value inferred from the post-merger signal. The predictions and signal-based estimates are compatible within the reported uncertainties. In the main analysis, the entropy difference is consistent with zero within a 68% credible interval, and changing selected analysis choices reveals no compelling disagreement. This is a successful consistency test for one event, not proof that the proposed rule governs all mergers.

Young explorerTwo black holes joined together to make one bigger black hole. Scientists tested an idea about which kind of black hole would be left over. The idea uses a number called entropy and says the new black hole should have as much of it as the rules allow. They used the waves from one merger to compare what the idea predicted with what they could work out about the new black hole. The answers were close enough that they found no clear disagreement. That is a clue the idea might work, but it does not prove it.

Gravitational-Wave Microlensing as a Probe of Compact Object Population

Eungwang Seo, Jose María Ezquiaga, Martin Hendry

• General Relativity and Quantum Cosmology
• Data Analysis, Statistics and Probability

AstronomerThe authors develop a hierarchical Bayesian framework to infer the power-law microlens mass-function slope α_ML, lens number density n₀, and compact-lens dark-matter fraction f_DM from an ensemble of microlensed gravitational-wave signals. Wave-optics signatures offer a probe of poorly constrained lens populations over roughly 1–10⁵ solar masses, including electromagnetically faint populations. Tests using simulated signals from a realistic binary black hole population indicate that about 100 detected microlensed events can constrain α_ML and n₀, though a degeneracy remains. For an assumed low-mass-dominated population with α_ML = 2 and n₀ = 10⁶ Mpc⁻³, the simulations predict about 130 detectable microlensed events over three years at O4 sensitivity. In this scenario, the framework recovers the injected f_DM ≃ 1.2 × 10⁻⁴, with a 90% credible interval of 7.3 × 10⁻⁵–1.8 × 10⁻⁴. These are simulation-based forecasts and recovery tests, not observational measurements of a lens population.

PublicObjects that give off little or no light are difficult to count. This study proposes using the distortions they can imprint on gravitational waves from merging black holes to estimate how common such objects are, how their masses are distributed, and what fraction of dark matter they represent. The researchers developed a statistical method and tested it on simulated signals. About 100 detected signals affected by this gravitational microlensing could constrain both the lens mass distribution and abundance, although some combinations of those properties would remain difficult to distinguish. For one assumed population dominated by lower-mass lenses, the simulations predict about 130 detectable events in three years at O4 sensitivity and recover the dark-matter fraction put into the simulation, with a range of uncertainty. The study does not report an observed population or a measured dark-matter fraction.

Young explorerSome things in space are hard to see because they give off little or no light. But their gravity can change passing ripples in space, leaving clues that they are there. The scientists made pretend ripple signals on a computer and tested a way to read those clues. Their tests suggest that about 100 changed signals could help tell how many hidden things there are and how heavy they are, though there would still be some guessing. They have tested the idea with pretend signals, not counted real hidden objects this way.

Euclid: Survey mask effects on clustering of galaxy clusters

A. Fumagalli, R. Ingrao, M. Costanzi+97 more

AstronomerUsing DR1-like lightcone mocks rather than survey observations, the authors assess how Euclid’s survey mask and spatially varying cluster selection affect the cluster two-point correlation function and its covariance. The irregular footprint produces no appreciable change in the correlation function when the random catalogue uses the same mask. Patchwise selection variations do not significantly bias the clustering amplitude even at levels well above those expected for DR1. Once inhomogeneity becomes large enough to matter, the effect depends on the maximum selection-function variation between regions rather than their number. Both irregular geometry and non-uniform coverage increase the covariance through small, nearly scale-independent offsets that can be captured by nuisance parameters in the covariance model. These simulation results support the treatment of mask systematics for DR1 and guide refinements for future Euclid cluster analyses.

PublicThe researchers used simulated catalogues resembling Euclid’s planned first data release to test whether uneven sky coverage could distort measurements of how galaxy clusters are grouped. In these tests, an irregular survey boundary did not appreciably change the measured clustering when the comparison catalogue used the same boundary. Differences in how clusters were selected across the sky also caused no significant bias, even when those differences were much larger than expected for the first release. At more extreme levels, the distortion depended on the largest selection difference between regions, not on how many regions there were. Both kinds of uneven coverage did, however, slightly increase the uncertainties and correlations in the measurements. The authors find that these changes can be accommodated in the uncertainty model; the findings are simulation tests, not results from Euclid observations.

Young explorerScientists want to learn how groups of galaxies gather together. But a sky map can have a wiggly edge, and some parts may be better at finding galaxy groups than others. They tested pretend maps like the ones Euclid is expected to make. The wiggly edge did not noticeably spoil the grouping measurement when they gave their comparison map the same edge. Uneven searching did not spoil it much either, unless the differences became very big. Both problems made the answers a little less certain, and the scientists found a way to include that extra uncertainty in their calculations.

Primordial Black Holes and Induced Gravitational Waves from Inflation with History-Dependent Effective Dissipation

Narges Rashidi

• High Energy Physics - Phenomenology

AstronomerThis theoretical study modifies inflation with an exponential prefactor multiplying the scalar Lagrangian, dependent on accumulated expansion through a field-dependent coupling. Varying the full finite-interval action introduces an adjoint response with a final-time boundary condition. The authors derive background and coupled scalar perturbation equations and examine five benchmarks using an exponential plateau potential and a smooth single-window coupling. Near-cancellation among kinetic, direct-coupling and adjoint terms produces transient positive minima in ε₁ without a comparable decrease in field velocity. CMB-pivot-normalized scalar spectra have localized peaks of 0.033–0.098. Assuming Gaussian statistics and the adopted radiation-era collapse prescription, predicted primordial-black-hole abundance peaks occur at masses from 4.52 × 10⁻¹³ to 34.05 solar masses. The lightest benchmark reaches f_PBH ≈ 0.99 within the monochromatic approximation. Predicted scalar-induced gravitational-wave peaks span 6.78 × 10⁻¹⁰–5.92 × 10⁻³ Hz, with selected benchmarks within projected future-detector sensitivities. These are model predictions, not detections.

PublicCould changes to the earliest expansion of the universe produce black holes that account for dark matter? This theoretical study explores five examples of an inflation model in which a field’s behavior depends on the accumulated expansion. The calculations produce enhanced fluctuations that could later form primordial black holes, with predicted abundance peaks at masses ranging from tiny fractions of the Sun’s mass to about 34 solar masses. In the lightest example, these black holes could account for nearly all dark matter—but only under the study’s assumptions about fluctuation statistics and collapse, and an approximation treating the black holes as having one mass. The model also predicts gravitational waves, with some examples potentially accessible to future detectors. Neither the black holes nor these gravitational waves are reported as observed.

Young explorerScientists used math to explore an idea about how the universe grew very fast when it was young. In their model, little bumps could grow into black holes and also make ripples in space. One example suggests the black holes might explain almost all the mysterious stuff called dark matter, but that depends on simplifying assumptions. These are predictions, not things the scientists have found.

Horndeski Gravity as an Effective Dark Energy Fluid in Cosmological N-body Simulations

Vicente Pedreros Aballay

AstronomerThe authors implement modified gravity as an effective dark-energy fluid in the N-body code CONCEPT, replacing its CLASS solver with mochi_CLASS to support Horndeski models. Linear effective-fluid density, pressure, velocity-divergence and anisotropic-stress perturbations are expressed through synchronous-gauge metric perturbations and evolved using the Boltzmann equation. Simulations cover w0waCDM, Hu–Sawicki f(R) and cubic Galileon scenarios, all including massive neutrinos. The authors report relative differences from General Relativity close to linear-regime predictions: below 0.2% for ΛCDM, up to 40% for f(R), and below 25% for cubic Galileon. The abstract does not specify the statistic underlying these percentages. These are simulation findings, not observational constraints; the dark-energy perturbations remain linear, and the authors emphasize that validating the implementation is computationally nontrivial. The code is intended to enable broader exploration of modified-gravity models for cosmological surveys.

PublicCould changing our theory of gravity help explain the Universe’s accelerating expansion? This study develops a computer tool to explore that possibility, representing changes to gravity as an effective dark-energy fluid. The researchers simulate several cosmological models, each including massive neutrinos, and report differences from standard gravity broadly consistent with predictions made in the linear approximation. Their treatment of the effective dark-energy disturbances is also linear, so it is not a fully nonlinear calculation of modified gravity. These are computer results, not evidence from observations that gravity must be changed. The authors stress that validating the new code is challenging and present it as a tool for future studies using cosmological surveys.

Young explorerThe Universe is growing, and scientists want to understand why it is growing faster. They made a computer tool to try out different rules for gravity and watch how matter gathers together. The computer worlds behaved differently, but that does not prove the real Universe uses different rules. The tool still needs careful checking.

Planting neutrino SE-EdS: A < 3% accurate clustering approximation for neutrinos and other hot dark matter

Amol Upadhye, Yvonne Y. Y. Wong

• High Energy Physics - Phenomenology

AstronomerThe authors present SE-EdS, a linear approximation for non-relativistic neutrinos and other hot dark matter, motivated by degeneracies between neutrino mass and other cosmological parameters in scale-dependent clustering analyses. It is exact in the linear Einstein-de Sitter case and is reported to have less than 3% error at all length scales across a broad range of flat and curved cosmologies with 0.2 ≤ Ωm,0 ≤ 1, 0 ≤ Ων,0 ≤ 0.018, −0.1 ≤ ΩK,0 ≤ 0.1, and w0 ≤ −0.6. Its broad matter-density coverage is suited to N-body simulations spanning z ≲ 100. The authors propose adding neutrinos to simulations in Fourier space: when neutrinos contribute at most 3% of the matter, they state that the approximation's error implies less than 0.1% error in the total matter density contrast, at negligible computational cost. They quantify its accuracy, explore connections to higher-order corrections in existing linear-response schemes, and provide an online implementation. These are approximation and modeling results, not observational measurements.

PublicNeutrinos complicate calculations of how matter clumps in the universe because their effects can be confused with those of other cosmological properties. This paper introduces SE-EdS, a simplified calculation for neutrinos moving much slower than light and for other hot dark matter. The authors report errors below 3% across all length scales for a broad, specified range of universe models; the method is also exact in one special linear model. They propose using it to add neutrino effects cheaply to computer simulations. If neutrinos make up no more than 3% of the matter, they state that the resulting error in the total matter density contrast—a measure of clumpiness—is below 0.1%. This is a computational method, not a new observation or measurement of neutrino mass.

Young explorerScientists use computers to work out how matter gathers into clumps in space. Tiny particles called neutrinos can change those clumps, but including them can make the math harder. This paper gives scientists a shortcut for certain kinds of calculations, when the neutrinos move much slower than light. The authors say the shortcut makes only small mistakes in many models of the universe. They suggest using it to help computers include neutrinos without much extra work. It is a new way to calculate things, not a new discovery made by looking at the sky.

Cosmological Backreaction and the Separate Universe Conjecture: Dynamical volume partitioning of Newtonian cosmologies

Thomas Buchert, Jan J. Ostrowski, Alfred Bovon

AstronomerThis theoretical work develops an exact, dynamical volume-partitioning framework for Newtonian cosmologies with collisionless matter, using cosmological backreaction to relate structure inhomogeneities to averaged properties. It provides a tool for potential simulation applications and for imposing regional analytical assumptions consistently with global integral constraints. Examining separate-Universe approaches, the authors use AvERA to show that identifying locally assigned Friedmannian rates with physical regional expansion rates is constrained by the global Newtonian 3-torus condition. If simulation cells instead represent non-material control volumes, Reynolds transport introduces mass-flux and flux-backreaction terms, so their dynamics generally cannot be treated as independent Friedmann domains. The paper also discusses consistency conditions for stable-clustering prescriptions; it reports a theoretical framework rather than observational findings.

PublicThe paper develops an exact mathematical way to divide a Newtonian model of the universe into evolving regions while keeping their behavior consistent with the model as a whole. This can help researchers study how uneven clumps of matter interact with average cosmic properties. The authors examine approaches that treat regions somewhat like separate universes. Using the AvERA approach as an example, they show that assigning each region its own expansion rate must respect constraints from the overall model. If matter can cross the boundaries of simulation cells, its flow adds terms that generally prevent the cells from evolving as independent miniature universes. These are theoretical consistency results and tools for possible simulation work, not new observations.

Young explorerImagine a pretend universe on a computer, split into little boxes. The scientists worked out math rules to keep what happens in the boxes consistent with what happens in the whole pretend universe. They explain that you cannot usually let every box grow as if it were a tiny universe all by itself. If matter moves between boxes, the rules must count that movement too. This is work about making universe models fit together, not a new discovery seen in the sky.

Magnetohydrodynamics During Reheating

Sovan Sau, Subhasis Maiti, Sahel Dey+2 more

AstronomerThe authors develop a three-dimensional nonlinear multifluid MHD framework for non-instantaneous reheating through perturbative inflaton decay into a radiation plasma. In the simplified case of spatially homogeneous energy injection, their modeling finds increased radiation and kinetic energy densities without significant amplification of the initial magnetic-field perturbations. The magnetic spectrum remains largely unchanged relative to instantaneous reheating, whereas velocity perturbations redistribute across scales, affecting the resulting gravitational-wave spectrum. These are theoretical findings, not observational measurements; inhomogeneous decay and detailed thermalization effects remain directions for future investigation.

PublicThis theoretical study explores reheating, the transition from cosmic inflation to the hot Big Bang, when energy from the field driving inflation feeds a hot plasma. The authors model how the plasma's motion, magnetic fields, and gravitational waves evolve when that energy is supplied uniformly through space over time. In this simplified model, the energy supply raises the radiation and motion-related energy densities but does not substantially strengthen the initial magnetic-field variations. Compared with an instantaneous transition, the distribution of magnetic power across scales stays largely unchanged, while changes in plasma motion affect the predicted gravitational-wave spectrum. The study does not report observations, and more realistic, uneven energy release and detailed thermalization remain to be explored.

Young explorerScientists used a model to study a time when the very young universe was filling with hot stuff. In their model, energy was added evenly everywhere, a little at a time. The hot stuff gained energy and more energy went into its motion, but tiny differences in its magnetic field did not grow much stronger. The pattern of motion changed, which changed the model's ripples in space, called gravitational waves. This is what a simplified model says, not something the scientists watched happen.

Shining LIMelight into the dark: Probing Dark matter - baryon interactions with Line Intensity Mapping

Durba Ghosh, Ranjini Mondol, Ranjan Laha

• High Energy Physics - Phenomenology

AstronomerThis study forecasts the sensitivity of the upcoming COMAP-EoR and COMAP-ERA line-intensity mapping surveys to elastic dark matter–proton and dark matter–electron scattering. Momentum and heat exchange suppress structure formation, imprinting signatures on the linear matter power spectrum that propagate to the LIM power spectrum (PS) and voxel intensity distribution (VID). The authors consider momentum-transfer cross sections proportional to v^n for n = 0, -2, and -4, representing contact, electric dipole-moment-like, and Coulomb-like interactions. Fisher forecasts using the VID alone, with the 16 and 30 GHz observed bands combined, project sensitivities stronger than existing cosmological limits for n = -2 and -4 at sub-GeV dark matter masses. The study also explores combining PS and VID. These are projected capabilities, not observational constraints or detections, positioning LIM as a complementary probe of dark matter interactions.

PublicCould dark matter exchange heat and motion with ordinary matter? This study investigates whether future maps of carbon monoxide emission could test that possibility. Such interactions could suppress the formation of cosmic structures and alter the patterns and brightness distributions in these maps. Using statistical forecasts for the upcoming COMAP-EoR and COMAP-ERA surveys, the researchers predict that brightness distributions measured across two observing bands could test some interaction models more sensitively than existing cosmological limits, for dark matter particles with masses below one GeV. They also explore using brightness distributions together with spatial patterns. The work predicts what future surveys might reveal; it does not report a detection of dark matter interacting with ordinary matter.

Young explorerDark matter is something scientists study in space. This study asks what might happen if it bumps into ordinary matter and passes along heat or a push. That could change how groups of galaxies grow. Scientists calculated how future maps of glowing gas might help look for those changes. The maps could offer useful clues, but this study has not found those bumps happening.

The Start Time of Ringdown

Adrien Kuntz

• General Relativity and Quantum Cosmology
• High Energy Astrophysical Phenomena
• High Energy Physics - Theory

AstronomerThis theoretical analysis determines when quasi-normal-mode sums converge for a point particle plunging into a Schwarzschild black hole. A dynamical-amplitude model reproduces the waveform after the particle crosses the bounce radius, whereas a constant-amplitude sum converges only after t_S, corresponding to the advanced time at which the particle reaches the central singularity. For a plunge from the innermost stable circular orbit, t_S is approximately 9.4 M after the peak of the 22 mode. After t_S, the dynamical- and constant-amplitude models are equivalent. The analysis also implies that any direct-wave contribution must reduce to the late-time tail after t_S.

PublicThis mathematical study examines when a non-spinning black hole’s gravitational-wave signal, produced by a plunging point-like particle, can be represented by adding its characteristic ringing patterns. A model that lets the strengths of those patterns change with time reproduces the signal after the particle passes a particular radius. A sum with fixed strengths converges only after a later threshold, tied mathematically to the particle reaching the central singularity. Beyond that threshold, the two descriptions are equivalent. The analysis also implies that any separate direct-wave contribution must then reduce to the signal’s lingering late-time tail. These are theoretical findings, not observations.

Young explorerThe researchers used math to study a tiny object falling into a black hole that does not spin. They tried building the wave signal by adding ringing notes together. Letting the notes change their loudness works from an earlier point in the fall. Keeping their loudness fixed works only later. After that later time, both recipes give the same answer, and any separate direct part of the wave must become just its fading tail. This was a math study, not something the researchers watched happen.

The Cosmology of Hawking Axions

Abdelaziz Hussein, Gordan Krnjaic, Sarunas Verner

• High Energy Physics - Phenomenology
• General Relativity and Quantum Cosmology

AstronomerThe authors study boosted axion-like particles (ALPs) produced by Hawking evaporation during a hypothesized primordial-black-hole-dominated era. Because non-relativistic PBHs gain energy fraction relative to radiation, even a small initial abundance can lead to early matter domination, ending when evaporation restores the hot big bang. The resulting “Hawking axions” eventually become non-relativistic and decay into photons. The authors derive new constraints from their effects on big bang nucleosynthesis, the cosmic microwave background, large-scale structure, and X-ray observables. If the ALPs remain relativistic through recombination, their predicted contribution is ΔN_eff ≃ 0.05–0.11, depending on progenitor PBH mass, and may be detectable by future CMB probes. These are conditional predictions and constraints, not a detection of PBHs or ALPs.

PublicThe study explores a possible early universe in which primordial black holes briefly dominated its energy content before evaporating. In this scenario, evaporation would also produce fast-moving hypothetical particles called axion-like particles. These particles would eventually slow down and decay into light, potentially changing the formation of early elements, the universe’s ancient background light, the distribution of cosmic structure, and X-ray signals. The authors use these effects to place new limits on the particles, rather than report their discovery. If the particles were still moving at nearly light speed when the ancient background light was released, they would add a small amount of radiation whose size depends on the original black holes’ mass. Future measurements of that background light might detect this contribution.

Young explorerScientists are exploring a what-if story about the baby universe. What if it had black holes that disappeared and sent out tiny, very fast particles? Those particles could later slow down and turn into light. The scientists worked out limits on what these particles could be like by considering how they would change the universe. They have not found the particles. If the particles stayed fast long enough, future studies of the universe’s oldest light might reveal a clue.

Spacetime Evolution Induced by a Massive Cosmic String in Numerical Relativity

Yoshihiro Kishimoto, Cristian Joana, Teruaki Suyama

• General Relativity and Quantum Cosmology

AstronomerFull numerical relativity simulations investigate the formation of a high-tension, or “massive,” cosmic string in a radiation-dominated background under cylindrical symmetry. The simulated core undergoes topological inflation, while its boundary moves inward superluminally, causally disconnecting the core from the exterior. Oscillating string fields source an intermediate, nearly matter-dominated decelerating region bounded by a local maximum (“belly”) and minimum (“throat”) of the circumferential radius; the throat recedes outward at about 0.1c. An emitted gravitational wavefront marks the light cone of string formation, and even behind it the exterior lacks the conical structure associated with the static description. The authors construct a Penrose diagram from the simulations to represent the spacetime’s causal structure. These are numerical findings within the imposed symmetry, not astronomical observations.

PublicThe researchers used computer simulations to explore what might happen when a cosmic string—a one-dimensional defect that could form in the early universe—has exceptionally high tension. In their model of a radiation-dominated universe, with cylindrical symmetry imposed, the string’s core undergoes inflation. Its boundary moves inward faster than light, cutting off causal contact between the core and the outside universe. Oscillating string fields create a slowing, nearly matter-dominated region around the core, with a bulge and a narrow “throat”; the throat moves outward at about one-tenth the speed of light. The simulated string also emits a gravitational wavefront, and the exterior geometry differs from the cone-like shape expected in a static description. The researchers use these results to map which regions can communicate with one another. The study describes a simulated scenario, not a detected cosmic string.

Young explorerScientists used a computer to imagine a very strong, very thin string forming in the young universe. In their pretend universe, space inside the string grows very fast and becomes cut off from the space outside, so messages cannot travel between them. The space around it develops a bulge and a narrow place, and a ripple in gravity spreads outward. This is what happened in their computer model; it does not mean they found a real cosmic string.

Inflationary attractors in metric-affine gravity

Ilaria Andrei, Christian Dioguardi

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThis theoretical study examines single-field slow-roll inflation in metric-affine gravity (MAG), with an action linear in curvature and quadratic in distortion and with non-propagating torsion and non-metricity. Initially imposing projective invariance and scalar-dependent coefficients, the authors integrate out the non-dynamical distortion, obtaining a correction k(phi) to the scalar kinetic term. For xi-attractors, they find that strong coupling with finite distortion-coupling ratios to xi yields universal alpha-attractor predictions: n_s = 1 - 2/N_* and r = 12 alpha/N_*^2, where alpha = 1 + zeta/(6 xi) and zeta/xi encodes the distortion contribution. Starobinsky and Palatini inflation emerge as specific limits. A numerical parameter scan places almost all healthy points on either a Nieh-Yan-like attractor or the new MAG alpha-attractor. Dropping projective invariance preserves the large-field asymptotic structure; within the theory analyzed, the additional operators do not produce extra inflationary phenomenology. These are analytical and numerical model results, not observational findings.

PublicThe authors explore a theoretical description of inflation, an early period of cosmic expansion, using metric-affine gravity. They find that the extra geometric terms they study change the mathematical description of the field driving inflation. Yet, in a specified strong-coupling limit, a broad class of these models follows a common pattern of predictions, called an alpha-attractor, rather than giving unrelated answers. The pattern includes familiar Starobinsky and Palatini inflation models as special limits. In a numerical scan, almost all parameter choices judged healthy fell into one of two shared patterns. Removing an initially imposed symmetry did not change the large-field pattern or add new inflationary behavior within the theory studied. This work establishes relationships among theoretical models; it does not report observations confirming them.

Young explorerScientists used math to explore ideas about how the universe might have grown very quickly when it was very young. They tried different versions of the rules for gravity. Under the conditions they studied, many different versions gave predictions that followed the same pattern. Their computer calculations found that almost all the choices that passed their checks followed one of two patterns. This is a discovery about their math models, not proof that the universe really grew that way.

QUIJOTE scientific results -- XVIII. New constraints on the polarization of the Anomalous Microwave Emission in bright Galactic regions: ρOphiuchi, Perseus and W43

R. González-González, R.T. Génova-Santos, J.A. Rubiño-Martín+25 more

AstronomerNew QUIJOTE-MFI maps at 11, 13, 17 and 19 GHz, combined with ancillary data including WMAP and Planck, constrain anomalous microwave emission (AME) polarization in rho-Ophiuchi, Perseus and W43. Intensity SEDs spanning 0.4–3000 GHz are well described by free-free emission, thermal dust, AME and CMB anisotropies; polarized flux densities were extracted over 11–353 GHz. An improved intensity-to-polarization leakage correction enables reliable sub-percent constraints from Planck-LFI for the first time. The reported 95% confidence upper limits on the AME polarization fraction are 1.1% at 28.4 GHz in rho-Ophiuchi, 1.1% at 22.8 GHz in Perseus and 0.28% at 33 GHz in W43. At 17 GHz, the corresponding limits are 5.1%, 3.5% and 0.85%. Stacking maps across 10–60 GHz reduces statistical noise and yields final limits of 0.58%, 1.64% and 0.31%, respectively. These are upper bounds, not measurements of a nonzero polarization fraction, and not all are below 1%. The authors report the most stringent constraints to date for these three regions, relevant to assessing AME contamination of future CMB polarization observations.

PublicResearchers studied how strongly an unusual microwave glow, called anomalous microwave emission, is polarized—whether its waves favor a particular orientation. This matters because the glow could interfere with future measurements of polarization in the cosmic microwave background. Using new QUIJOTE maps alongside other observations, including WMAP and Planck, they examined three star-forming regions in our Galaxy: rho-Ophiuchi, Perseus and W43. Correcting instrumental leakage and combining maps at different frequencies helped them set tight upper bounds rather than measure a definite polarization level. Their final combined-map limits are 0.58%, 1.64% and 0.31%, respectively, at 95% confidence. The authors describe these as the strongest constraints yet for these regions; they do not establish that the emission is completely unpolarized.

Young explorerScientists looked at an invisible glow from three places in our galaxy where stars form. They wanted to know how much the glow’s waves line up in the same direction. They used several sets of sky maps, corrected a problem in the measurements, and combined maps to make the glow easier to study. They found tight limits on how much the waves could line up, but that does not mean they proved there is no lining up at all. Knowing this can help scientists study another glow in space called the cosmic microwave background.

Wide Area VISTA Extragalactic Survey (WAVES): Redshift-limited selection of targets for the Wide survey using decision-tree classification

G. Kaur, M. Bilicki, S. Bellstedt+11 more

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe authors present an XGB classifier for selecting WAVES-Wide targets from nine-band VST+VISTA photometry. Rather than estimating individual photometric redshifts, it assigns probabilities that galaxies lie below the subsurvey limit of z=0.2. Training and testing use a comprehensive spectroscopic sample overlapping the WAVES fields. Tests at the fiducial selection limits and nearby redshift and magnitude thresholds yield purity and completeness of roughly 90–95%, depending on the test set; performance worsens near the selection boundaries and on DESI-selected test samples not used in training. Applied to 8.6 million photometric galaxies, the classifier produces about 1.2 million target candidates, or 1 million with P_XGB(z≤0.2)>0.72. These are candidate selections, not newly measured redshifts, which will come from 4MOST. The results demonstrate the potential of classification-based selection but do not establish uniform achievement of WAVES's 95% completeness requirement.

PublicThe researchers tested a machine-learning method to help choose galaxies for WAVES-Wide, a survey that needs a highly complete sample within a specified brightness and distance range. Using measurements in nine light bands and examples with known redshifts, the method estimates whether each galaxy falls below the survey's redshift limit, rather than estimating its exact redshift. Tests found that roughly 90–95% of selected galaxies met the criteria and roughly 90–95% of eligible galaxies were recovered, depending on the test sample. Performance was worse near the selection boundaries and on a separate DESI test sample not used for training. Applying the method to 8.6 million galaxies produced about 1.2 million candidates, narrowed to 1 million with a stricter probability cutoff. These are targets for future redshift measurements with 4MOST, not a million newly confirmed survey members.

Young explorerThe scientists want to choose galaxies for a big space study. They taught a computer using galaxy light and examples whose distances were already known. The computer then guessed which other galaxies were close enough to be picked. It worked well in tests, but it made more mistakes with some groups of galaxies and with galaxies near the choosing rules. It helped make a list of about a million galaxies to check. Scientists still need to measure them to find out which ones really belong.

Euclid: Modelling observational effects in cluster counts and cluster clustering

A. Fumagalli, M. Costanzi, T. Castro+97 more

AstronomerUsing 1000 Euclid-like cluster catalogues, this modelling study examines systematic effects on cluster counts, clustering, and their auto- and cross-covariances, and provides prescriptions for joint analysis. Likelihood analyses targeting Ωm and σ8 find that combining counts and clustering increases the figure of merit by over 300% relative to counts alone. In these catalogues, the probes are uncorrelated, and joint constraints are nearly insensitive to the cosmology dependence of the covariance. Photometric-redshift uncertainties broaden posteriors by 20–30%. Redshift-space distortions have smaller effects on posterior widths—5% for clustering alone and 10% for the joint analysis—but can significantly bias constraints if omitted. Clustering below 60 h⁻¹ Mpc adds constraining power, whereas scales beyond the acoustic oscillation scale add almost no information on these two parameters. Redshift-space distortions and photometric-redshift uncertainties also affect the count covariance, changing parameter constraints by about 15–20%. These are catalogue-based assessments for Euclid, not reported observational constraints.

PublicA study using 1000 simulated catalogues resembling the Euclid survey tests how galaxy clusters could help measure the Universe's matter density and the strength of matter clustering. Combining how many clusters there are with how they are arranged improves a statistical measure of constraining power by more than 300% compared with counting clusters alone. The simulations also show why measurement and modelling uncertainties matter: uncertainty in distances estimated from light-based redshifts broadens the inferred ranges of cosmological parameters by 20–30%. Distortions in apparent cluster positions caused by their motions have smaller effects on the widths of those ranges, but ignoring them can substantially shift the answers. Smaller-scale cluster patterns add useful information, while patterns larger than the acoustic oscillation scale add almost none for the two parameters studied. These findings guide future Euclid analyses rather than report measurements from the survey.

Young explorerScientists made 1000 pretend maps like the ones a space survey called Euclid could make. The maps show groups of galaxies. In their tests, counting the groups and looking at how they are spread out together gave better clues about the Universe than counting alone. But fuzzy guesses about how far away the groups are, and the way the groups move, can make the clues less clear or lead to wrong answers if ignored. These tests help scientists plan how to study real maps; they are not new measurements of the real Universe.

Einstein-Cartan pseudoscalaron inflation, reheating and nonthermal leptogenesis

Carlo Di Benedetto, Alessandro Di Marco, Emanuele Orazi+1 more

• High Energy Physics - Phenomenology
• High Energy Physics - Theory

AstronomerThis theoretical study examines postinflationary dynamics in Einstein-Cartan pseudoscalaron inflation coupled to a type-I seesaw extension with three heavy right-handed Majorana neutrinos. The authors find that nonthermal leptogenesis is necessary and self-consistent within this framework, principally because of the inflaton’s universal coupling to the heavy Majorana fermions. They report predictions compatible with cosmic microwave background, baryon acoustic oscillation, Big Bang nucleosynthesis, and neutrino oscillation constraints over a wide range of the Barbero-Immirzi parameter γ. For γ ≈ −1/100 and a lightest Majorana-neutrino mass ≳ 10^13 GeV, they obtain n_s ≈ 0.970, r ≈ 0.004, N_e ≲ 60, and n_B/s ≈ 8.7 × 10^−11. These are model predictions, not new observational measurements.

PublicWhy does the Universe contain more matter than antimatter? This theoretical study connects that puzzle to a model of the Universe’s early rapid expansion and three proposed heavy neutrinos. Within the model, interactions between the field driving expansion and those particles make a process called nonthermal leptogenesis necessary for producing the observed matter imbalance. The authors find that the model can agree with several cosmological measurements and neutrino experiments across a broad range of one of its key parameters. This agreement supports the model’s viability, but does not establish that these particles or this mechanism actually shaped our Universe.

Young explorerThe Universe has more matter—the stuff stars and people are made of—than antimatter. Scientists studied a possible story about why. In their story, the Universe’s very early stretching is linked to three kinds of very heavy particles, which help explain the extra matter. Their calculations fit what we know about the Universe, but we do not yet know whether this story really happened.

Revisiting the Lyth bound constraints on inflation from ACT DR6 results

Rui Yang, Jun Tao, Peng Wang+1 more

• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors revisit Lyth-bound constraints on inflationary tensor amplitudes under a sub-Planckian inflaton field-excursion requirement. They contrast a conventional derivation assuming a scale-invariant curvature spectrum, n_s = 1, with observations favoring a red tilt. Adopting the scalar spectral index n_s ≃ 0.9743 implied by ACT DR6, they derive a revised upper bound on the tensor-to-scalar ratio r. The abstract supplies no numerical value for that bound. The authors argue that it could exclude inflationary scenarios previously allowed under the n_s = 1 treatment; this is a potential theoretical consequence, not a reported observational exclusion.

PublicInflation describes a proposed period of rapid expansion in the early universe. This study revisits a theoretical limit on how strong inflation-generated gravitational waves could be relative to density fluctuations. The authors update their calculation using recent Atacama Cosmology Telescope results, which favor a fluctuation spectrum that varies with scale rather than the scale-independent spectrum assumed in the comparison calculation. They find a different upper limit, though the abstract does not give its numerical value. The revised limit could rule out some inflation models previously considered viable, but the abstract does not establish that any particular model has been ruled out.

Young explorerScientists have ideas about how the universe grew very fast when it was tiny. They used new clues from looking at space to redo a rule about how big its early ripples could have been. The changed rule might mean some ideas do not work, but they have not shown that here.

A derived evolution of dark energy from cosmic inhomogeneity confronted with baryon acoustic oscillations and type Ia supernovae

Jacky David Yang, Hans-Otto Carmesin

AstronomerThe authors derive H(z) for the volume dynamics of space framework, in which matter heterogeneity directly affects expansion. Using Planck inputs, the framework replaces the cosmological constant of flat ΛCDM with an effective dark-energy density that grows by 31% toward the present, predicts w(0) = -1.21 tending to -1 at high redshift, and gives an age of 13.52 Gyr, 0.3 Gyr below the homogeneous limit. Tests against DESI DR2 BAO and Pantheon+ supernovae leave the Hubble constant, sound horizon, and supernova absolute magnitude free, probing only the expansion-history shape. The prediction is disfavored relative to ΛCDM by Δχ² = 65 with one fewer parameter. Freeing the matter density reduces this to 42, but BAO and supernovae separately require incompatible matter densities of 0.35 and 0.54. Their combination constrains the heterogeneity amplitude to σ8 < 0.14 at 95% confidence, versus the Planck input of 0.81, and favors the model’s homogeneous, flat-ΛCDM limit. At the leading order evaluated, this heterogeneous contribution cannot resolve the Hubble tension and produces dark-energy evolution opposite to that favored by current distance data.

PublicThis study tests a framework in which the uneven distribution of matter directly changes how the universe expands. Its calculations predict that the effective dark-energy density increases toward the present, rather than staying constant as in the standard model. The authors compare the predicted pattern of expansion with DESI DR2 measurements of baryon acoustic oscillations and Pantheon+ measurements of exploding stars, allowing the overall distance calibration to vary. Together, these data favor the standard model over the framework’s prediction. Allowing the matter density to vary improves the fit, but the two datasets require incompatible values when fitted separately. The combined data favor the framework’s limit with no heterogeneous contribution. At the level of approximation studied, this proposed effect cannot explain the Hubble tension, the disagreement over the universe’s present expansion rate, and changes dark energy in the opposite direction to that favored by current distance measurements.

Young explorerThe universe is getting bigger, and its matter is spread out in lumps. Scientists tested an idea that these lumps could change how fast the universe grows. They worked out what the idea predicts and compared it with measurements of space. The measurements fit the usual explanation better than this new idea. In the version they tested, the lumps do not solve a puzzle about how fast the universe is growing.

Boosted Odds: Lower-Point Probes of Parity Violation with Momentum Fields

Yong Sheng Yap, William R. Coulton, Jiamin Hou+1 more

• High Energy Physics - Phenomenology

AstronomerThe authors propose the density-density-momentum bispectrum, with momentum p = (1 + δ)v, as a probe of primordial parity violation associated with inflation beyond single-field slow roll. It complements density four-point statistics while reducing the dimensionality of the data vector and covariance analysis. They show that parity sensitivity survives projection of momentum onto the line of sight. A Fisher forecast for the parity-violating amplitude of an ultra-squeezed template in the galaxy-galaxy-kSZ bispectrum predicts constraints competitive with existing methods; this is not an observational detection. The proposed analysis could leverage existing pipelines and ongoing work on systematics mitigation and covariance modelling.

PublicThe researchers propose a new way to look for signs that the early universe behaved differently from its mirror image. Such a pattern could point to inflationary physics beyond a standard model involving a single slowly evolving field. Their method combines two measures of matter density with one measure of motion weighted by density, offering a less complex analysis than traditional searches using four density measurements. They show that the method remains sensitive even when only motion along our line of sight is accessible. A statistical forecast combining galaxy clustering with kinetic Sunyaev-Zel'dovich microwave patterns suggests that it could compete with existing methods. The paper proposes and assesses a search technique; it does not report finding this early-universe asymmetry.

Young explorerImagine holding the universe up to a mirror and asking whether it follows the same rules in the reflection. Scientists have suggested a new way to look for clues from when the universe began, using where galaxies gather and information about motion. Their calculations suggest the idea could work about as well as other ways of looking. They have not found a mirror mismatch; they are explaining a new way to search for one.

Cosmologically viable non-polynomial quasi-topological gravity: explicit models, ΛCDM limit and observational constraints

Emmanuel N. Saridakis

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThe authors study a subclass of non-polynomial quasi-topological gravity in which a single function of the Hubble parameter determines the cosmological background dynamics. This extension of general relativity includes higher-curvature effects while retaining second-order field equations and avoiding higher-derivative instabilities. They derive cosmological viability conditions and construct several functional realizations. Detailed late-time analyses of the quartic and power-law models yield a matter-dominated epoch followed by dark-energy domination, with an effective geometric dark-energy component whose evolving equation of state can occupy the quintessence or phantom regime. Bayesian MCMC comparisons with Type Ia supernova, cosmic chronometer, and baryon acoustic oscillation data find both models compatible with the observations, with fit quality comparable to ΛCDM. These results establish viable theoretical alternatives for late-time expansion, not statistically significant observational evidence for departures from ΛCDM.

PublicCould the Universe’s accelerating expansion be described by a change to gravity? This study explores theoretical models in which effects from spacetime curvature act like an evolving form of dark energy. Two models examined in detail produce a period dominated by matter followed by one dominated by dark energy. The researchers compared these models with supernova observations and other measurements of cosmic expansion. Both fit the selected data about as well as the standard cosmological model, ΛCDM. That makes them possible alternatives, but the observations do not provide statistically significant evidence that either improves on or replaces the standard picture.

Young explorerThe Universe is getting bigger, and its growing is speeding up. Scientists tried new gravity ideas that might explain this. Two of their ideas matched measurements about as well as the usual explanation. That means the new ideas might work, but the measurements do not show that they are better than the usual one.

Tachyonic Encore: A universal shift of inflationary observables

Diogo S. Gorgulho, Margherita Putti, Rodrigo Gonzalez Quaglia+3 more

• High Energy Physics - Theory
• General Relativity and Quantum Cosmology
• High Energy Physics - Phenomenology

AstronomerThe authors propose a gravitational multi-field mechanism in which a light axion spectator, initially near its potential hilltop, modifies the predictions of single-field inflaton models. The axion remains frozen during inflation, leaving an effectively single-field background, but rolls afterward, turning the field-space trajectory and inducing transient tachyonic isocurvature phases entirely on super-horizon scales. This theoretical “tachyonic encore” produces a nearly scale-invariant enhancement of curvature power, suppresses the tensor-to-scalar ratio, and shifts the scalar tilt to a weighted combination of the adiabatic and entropic tilts at horizon crossing. The authors show that the mechanism can reconcile otherwise disfavored inflaton potentials with current CMB constraints. It also predicts local non-Gaussianity of order unity, potentially accessible to upcoming surveys; this is a prediction, not a reported detection.

PublicThe paper proposes a way to make some theories of the universe’s early rapid expansion compatible with current cosmic microwave background measurements. An additional light field, called an axion, would remain nearly still during that expansion and start moving afterward. Through gravity alone, its motion could strengthen the primordial density patterns on scales larger than the horizon, changing the balance between density fluctuations and gravitational waves and altering how the density patterns vary with scale. The authors show that this mechanism can bring otherwise disfavored models into agreement with current constraints. They also predict a particular departure from purely random, Gaussian patterns that upcoming surveys may be able to test. The mechanism is a theoretical proposal, not an observed event.

Young explorerScientists have an idea about what happened when the universe grew very fast. They imagine an extra ingredient that stayed still at first, then began to move after the fast growing stopped. In their theory, this could make tiny uneven patches stronger and help some ideas about the early universe fit what we see today. It could also leave a special pattern for future sky studies to look for. Scientists have not yet seen proof that this happened.

Primordial Black Holes from Vector-Induced Curvature Perturbations Sourced by Primordial Magnetic Fields

Chang Han, Zu-Cheng Chen, Hongwei Yu+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors propose a post-inflationary mechanism for enhancing small-scale curvature perturbations and producing primordial black holes during a stiff, or kination, epoch. Metric vector perturbations sourced by the vector component of primordial magnetic fields’ electromagnetic stress-energy remain approximately constant during kination, providing persistent nonlinear sources for second-order scalar perturbations. The resulting curvature power spectrum scales as P_R(k) ∝ k^-5, with amplification toward the infrared cutoff of the kination band. In a Ratra-type magnetogenesis realization, the authors find that the induced perturbations can yield enough primordial black holes to constitute a substantial fraction of dark matter. This is a theoretical mechanism and model-dependent possibility, not an observational detection.

PublicThe paper proposes a way that black holes could have formed in the very early universe and supplied a substantial fraction of dark matter. In the proposed scenario, an early phase called kination allows disturbances in gravity, driven by ancient magnetic fields, to persist and strengthen other ripples in the universe’s structure. Those amplified ripples could produce primordial black holes. The authors work through a particular model for generating the magnetic fields and find that this outcome is possible within it; they do not report observations establishing that it happened.

Young explorerThe scientists have an idea about how tiny black holes might have formed when the universe was very young. In their idea, magnetic fields helped some ripples grow strong enough to make black holes. Their calculations suggest that these black holes could make up a big part of the invisible matter called dark matter. But this is an idea they worked out, not something they have seen happen.

Precision Solar System Dynamics for Ultralight Dark Matter Search

Jonas Frerick, Hyungjin Kim, Felix Kling

• High Energy Physics - Phenomenology
• Earth and Planetary Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThe study assesses interplanetary radio ranging as a probe of ultralight dark matter through gravitational perturbations to solar-system dynamics. Ultralight dark matter has order-unity density fluctuations on its wavelength scale throughout the halo, which can perturb stellar and planetary motion. The authors find that current ranging precision could probe masses around 10^-15 eV if the solar-system dark matter density were 10^5 times the standard local dark matter density. This is a conditional sensitivity estimate, not a detection, and complements constraints from pulsar timing analyses.

PublicThe researchers explore whether precise radio measurements of distances between planets could help search for ultralight dark matter. This proposed form of dark matter would have density variations whose gravity could slightly disturb planetary motion. Their analysis indicates that present measurement precision could test particles with masses around 10^-15 electronvolts, but only if dark matter in the solar system were 100,000 times denser than the standard local dark matter density. The study does not report a detection; it assesses a search method that complements tests using pulsar timing.

Young explorerScientists wonder whether invisible stuff called dark matter could give planets tiny extra pulls. They studied whether very careful radio measurements of distances between planets could help find those pulls. For the kind they studied, today’s measurements could help only if there were much more dark matter near the Sun than the usual nearby amount. They have not found it this way; they are checking how the search might work.

Gravitational Wave Birefringence in generalized Palatini Chern Simons

Jose Perdiguero, Macarena Lagos

• General Relativity and Quantum Cosmology

AstronomerThis theoretical study examines parity-violating GW propagation in f(R) gravity coupled to a dynamical Chern-Simons (dCS) term, comparing metric and Palatini formulations. The model can support dynamical dark energy at the background level. For GW propagation, Palatini predicts both amplitude and velocity birefringence, while the metric formulation predicts amplitude birefringence only. Depending on the choice of f(R), its interactions can suppress or enhance birefringence. For the Hu-Sawicki, Exponential, and Hyperbolic models fitted to recent cosmological data, the predicted enhancement relative to f(R) = R is 1–10% in Palatini and up to a factor of two in the metric formulation. Existing GW birefringence constraints are translated into model-dependent bounds on the dCS coupling. The predicted effect grows polynomially with source redshift, unlike the linear-distance scaling commonly assumed in phenomenological treatments. These are model predictions and constraint translations, not a detection of birefringence.

PublicGravitational waves could change strength or travel at different speeds depending on their polarization if gravity distinguishes between mirror-image configurations. This paper explores that possibility mathematically in a modified theory of gravity, rather than reporting an observed effect. Two formulations of the theory give different predictions: one allows polarization-dependent changes in both wave strength and speed, while the other allows changes in strength only. The modification can either weaken or strengthen the effect, depending on its mathematical form. For three versions fitted to recent cosmological data, the predicted effect is stronger than in the reference theory: by 1–10% in one formulation and by as much as a factor of two in the other. The authors also use existing gravitational-wave limits to constrain a coupling in their model. Their predicted effect grows with source redshift in a more complicated way than the simple proportionality to distance often assumed.

Young explorerGravitational waves are ripples in space. Scientists used math to ask whether two kinds of these ripples might get stronger or weaker differently as they travel across the universe. In one version of their idea, the two kinds could also travel at different speeds. In another version, only their strength changes differently. The answer depends on which math they use. This is something their idea says could happen, not something they have seen happen.

How sky subtraction scales affect Intracluster light measurements

Giulia Golini, Sarah Brough, Mireia Montes+1 more

AstronomerRecovery of low-surface-brightness emission depends on survey depth and sky-background treatment. Estimating the sky on scales comparable to source sizes can bias flux measurements, particularly for extended intracluster light. The authors’ analysis in the M500–redshift plane indicates that sky-subtraction scales used in LSST Data Preview 2 and HSC-PDR3 affect clusters with M500 ≳ 10^13.4 solar masses at all redshifts, whereas HSC-PDR2 oversubtracts only the most massive systems at z < 0.1. The larger sky-subtraction scale anticipated for the full LSST survey is expected to mitigate, not necessarily eliminate, this bias.

PublicDeep images can reveal faint, spread-out light in galaxy clusters, but separating that light from the sky background is difficult. If the background is estimated over areas similar in size to the cluster’s glow, some real light can be mistakenly removed. The authors’ analysis indicates that the background-removal settings in LSST Data Preview 2 and one Hyper Suprime-Cam release, HSC-PDR3, affect a broad range of cluster masses at all redshifts. An earlier release, HSC-PDR2, removes too much light only for the most massive clusters at low redshift. A larger background-estimation scale planned for the full LSST survey is expected to reduce the problem.

Young explorerGroups of galaxies have a very faint glow spread around them. When scientists clean the bright sky background out of a picture, they can accidentally erase some of that glow too. The researchers found that some picture-cleaning settings can cause this problem for many galaxy groups and clusters. A change planned for a future survey should help keep more of the faint glow in the pictures.

CosmoVerse Data Challenge: How Tip of the Red Giant Branch Analysis Choices Shape the Inferred Hubble Constant

Siyang Li, Eleonora Di Valentino, Jackson Levi Said+62 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe CosmoVerse Data Challenge tested the sensitivity of TRGB-based Hubble-constant estimates to photometric-catalog selection, galaxy samples, and TRGB measurement settings within a shared distance-ladder framework. Its 26 submissions from 22 participants used a common SN Ia compilation, fitting procedure, and analysis notebook. The inferred H0 values had a median of 77.10 km s−1 Mpc−1, a standard deviation of 7.38 km s−1 Mpc−1, and a scaled median absolute deviation of 5.11 km s−1 Mpc−1; the latter two measures were about 3.4 and 2.4 times the typical quoted submission uncertainty, respectively. Differences in the measured TRGB of the anchor galaxy NGC 4258 also produced a coherent distance-scale shift. Because all submissions shared a notebook, many participants were trainees, and true galaxy distances are unknown, this spread measures sensitivity to participants’ analysis and sample choices, not a combined H0 determination or the systematic uncertainty of published TRGB measurements. Public notebooks and training supported an open examination of these choices.

PublicAstronomers use measurements of red giant stars and Type Ia supernovae to estimate how fast the Universe is expanding. The CosmoVerse Data Challenge asked participants to analyze public star catalogs while sharing the same supernova data and calculation framework. Different choices of catalogs, galaxies, and stellar measurements led to substantially different expansion-rate estimates across 26 submissions from 22 people. The middle estimate was 77.10 kilometers per second per megaparsec, and the spread was several times the uncertainty typically reported by an individual submission. Measurements of the reference galaxy NGC 4258 also shifted the distance scale. These results are not a new combined measurement of the expansion rate or a measure of the systematic uncertainty in published studies: participants shared an analysis notebook, many were trainees, and the galaxies’ true distances are unknown. Instead, the challenge shows how analysis choices can affect the answer and makes those choices easier to examine openly.

Young explorerScientists want to know how fast the Universe is growing. They use light from stars and exploding stars to help work out distances. In this challenge, people used the same computer notebook but made different choices about which star information and galaxies to study. They got different answers, even though they were following the same basic plan. That does not tell us which answer is right, because the galaxies’ true distances are not known. It helps scientists see why their choices matter and share how they do their work.

Searching for Signatures of i-process Nucleosynthesis in Metal-Rich, Lead-rich Barium Stars

Catherine Manea, Madeleine McKenzie, Gail Zasowski+6 more

• Solar and Stellar Astrophysics

AstronomerThe authors analyse six GALAH-selected stars with −0.7 < [Fe/H] < −0.1 and extreme Ba and Eu or Sm abundances, using Gemini/GHOST and McDonald/Tull spectra, and reanalyse two literature i-process candidates. They determine abundances for up to 42 elements, plus carbon and magnesium isotopic ratios, and compare them with barium stars, CEMP stars, and AGB model grids. Three stars have [Pb/Fe] = +1.79 to +2.50 dex, and two have [Eu/Fe] = +1.10 to +1.30 dex. Two of the three Pb-rich stars show patterns inconsistent with the compared s-process models and best explained by existing i-process predictions. The remaining sample is consistent with s-process enrichment or suggestive of atomic diffusion. Both literature candidates fit the i-process model, but s-process enrichment remains possible. These findings identify promising near-solar-metallicity i-process candidates and support a contribution from metal-rich AGB stars to elements classically attributed to the r-process, while motivating additional i-process modelling.

PublicAstronomers studied the chemical fingerprints of six stars selected for unusually large amounts of certain heavy elements and revisited two previously proposed candidates. Three stars stood out for their high lead abundances, and two showed exceptionally high europium abundances. In two of the lead-rich stars, the overall chemical patterns did not match the slow neutron-capture models tested and were best explained by predictions for an intermediate neutron-capture process, called the i-process. This makes them promising examples of that process operating in stars with iron contents approaching the Sun’s, rather than only in very iron-poor stars. The evidence is not conclusive for every target: other stars can be explained by slow neutron capture or may show effects of atomic diffusion, and the two previously proposed candidates still allow a slow-process explanation. More models are needed to clarify how much the i-process contributes to the Milky Way’s chemical makeup.

Young explorerStars have different mixtures of ingredients. Scientists looked at light from some stars and found that a few had lots of heavy ingredients, such as lead. They compared these mixtures with computer predictions for different ways stars can make heavy ingredients. For two stars, one special recipe matched best, while the slow recipe they tested did not fit. That is a clue, not proof that every star used the special recipe. Scientists need more computer recipes to understand what happened.

Dynamics of self-gravitating halos with decaying dark matter

Anna Bencke, Marc Kamionkowski, Annika H. G. Peter+1 more

• Cosmology and Nongalactic Astrophysics
• High Energy Physics - Phenomenology

AstronomerThis simulation study uses NSphere to evolve self-gravitating spherical halos in a model where dark matter decays into a slightly less massive daughter and a massless particle. Recoil of the daughter heats the halo; when the kick velocity is small relative to the halo’s characteristic velocity, the halo remains bound but expands. The authors also model anisotropic initial conditions, reporting non-negligible effects on the final density profile. Across a broad range of decay times and kick velocities, they train an emulator mapping decay parameters to relaxed density profiles. The predicted halo-scale signatures are discussed as complementary to existing cosmological constraints and testable with upcoming surveys, rather than as observational evidence for dark matter decay.

PublicThe researchers simulate what could happen to spherical dark matter halos if their particles slowly decay into a slightly lighter particle and a massless particle. Each decay gives the lighter particle a small kick, heating the halo. In the simulations, kicks that are small compared with the halo’s typical internal speed make it expand without becoming unbound. The team also finds that the final distribution of dark matter depends noticeably on whether the particles’ initial motions favor some directions over others. They train a computational tool to connect decay properties with the halo’s eventual density profile. These are model predictions, not observed signs of decay; future surveys could test them alongside existing constraints.

Young explorerThe scientists used a computer to imagine a round cloud of dark matter. In their model, a dark matter particle changes into two particles, giving one a little kick. Small kicks make the cloud puff up while gravity still holds it together. The computer also shows that how the particles move at the start matters for how the cloud ends up. This does not show that real dark matter changes this way. Future studies of the sky could help test the idea.

Euclid. Predicting scaling relations for emission-line galaxies using simulated data

Euclid Collaboration, C. Mancini, L. Gabarra+97 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis simulation-based forecast assesses recovery of the star-forming main sequence (MS), dust-mass relation (DMR), and mass-metallicity relation (MZR) by the Euclid Wide and Deep Surveys at final DR3 depth, using MAMBO mock spectra processed through the official Euclid pipelines. Paβ, Hα, and [OII] trace the MS across 0 ≤ z ≤ 4. The Wide Survey preferentially selects bright, strongly star-forming galaxies, biasing the MS toward higher normalisation and a flatter slope. The Deep Survey provides almost complete Paβ- and Hα-based sampling at log10(M*/M☉) ≥ 10.3 over 0 ≤ z ≤ 1.88, with mild biases at the redshift boundaries; [OII] selection increasingly favours high SFRs at the highest redshifts. Balmer-decrement measurements probe the DMR over 1.45 ≤ z ≤ 1.88 in Wide and 0.9 ≤ z ≤ 1.88 in Deep. Recovered colour excesses agree well with inputs, but Hβ detection selects less obscured galaxies at fixed stellar mass, especially in Wide. A multiple-line golden sample at 1.49 ≤ z ≤ 1.88 recovers gas-phase metallicities with typical accuracy of 0.1 dex above log10(M*/M☉) = 10, with biases up to 0.15 dex below this mass. Relative to an H-band-limited sample, it favours the upper MS and lower MZR. These are forecasts, not observational results; omitted mutual spectral contamination and detector persistence limit the simulations' realism.

PublicHow faithfully will Euclid reveal the connections between a galaxy's stellar mass, star formation, dust obscuration, and gas composition? Researchers tested this with simulated spectra, not new galaxy observations. Their forecasts suggest that Euclid's Wide Survey will favour the brightest, most actively star-forming galaxies, distorting the relationships inferred from them. The deeper Deep Survey should recover a much more complete picture for sufficiently massive galaxies over part of the simulated range. Dust estimates agree well with the simulated inputs, but requiring a faint hydrogen emission line excludes more heavily obscured galaxies, especially in the Wide Survey. A sample with several detectable emission lines also yields useful estimates of gas enrichment, although lower-mass galaxies show larger biases and the selection favours unusually active, less enriched galaxies. These forecasts provide a benchmark rather than a guarantee: the simulations omit effects including overlapping spectra and lingering detector signals.

Young explorerScientists made pretend galaxy light signals on computers to test what Euclid might learn. They found that an easier look mostly picks out bright galaxies making lots of stars. A deeper look should find a better mix, but some dusty galaxies can still be missed. That matters when learning how galaxies grow and what they contain. These are practice-test predictions, not discoveries from real galaxy observations, and the tests leave out some problems Euclid may face.

Euclid: Forecasting the number counts of bright line emitters in the Euclid Wide Survey and Euclid Deep fields

Euclid Collaboration, P. Cassata, S. Quai+97 more

• Cosmology and Nongalactic Astrophysics

AstronomerThis study forecasts emission-line galaxy counts for the Euclid Wide and Deep Surveys using semi-analytic models and empirical scaling relations, and tests spectral recovery with MAMBO lightcone spectra generated by FastSpec and processed through the official Euclid spectroscopic pipeline. Hα+[NII] counts are broadly consistent across mocks and with existing observations; relative RMS scatter in integrated Wide Survey predictions is approximately 19% for Hα+[NII], 44% for [OII], and 41% for [OIII]. In the simulations, correcting for flux losses and redshift misidentification recovers most intrinsic line counts, especially in the Deep Survey. MAMBO-based forecasts predict about 42 million Hα emitters in the Wide Survey and 1.7 million in the Deep Survey; corresponding [OII] and [OIII] forecasts are 1.3 and 7.5 million for Wide, and 0.5 and 0.8 million for Deep. These are predicted detections, not observed counts, and the oxygen-line forecasts carry substantial model-dependent uncertainty. The projected samples could extend large-scale structure and baryon acoustic oscillation studies beyond z≈2 and broaden Euclid's cosmology and galaxy-evolution reach beyond Hα alone.

PublicResearchers used galaxy models and simulated spectra to estimate how many galaxies Euclid could detect through distinctive lines of light from hydrogen and oxygen. They passed the simulated spectra through Euclid's official analysis software to test how well galaxy distances and line brightnesses could be recovered. One set of simulations predicts about 42 million hydrogen Hα-emitting galaxies in the Wide Survey and 1.7 million in the Deep Survey, along with millions of oxygen-line emitters across the surveys. These are forecasts, not new galaxy detections. Different models agree more closely on the combined Hα and nearby nitrogen-line counts, which also broadly match existing observations, than on oxygen-line counts. The oxygen forecasts therefore remain substantially uncertain. The predicted samples could help researchers study the Universe's large-scale structure and galaxy evolution farther back in cosmic history than Hα alone allows.

Young explorerEuclid will look at lots of galaxies far away. Scientists made pretend galaxy light on computers and tested how Euclid's software would read it. They predict Euclid could find millions of galaxies by spotting special kinds of light from hydrogen and oxygen. These are guesses based on computer models, not galaxies they have already found in these surveys. The models agree better about some kinds of light than others, so the real numbers could be different. Finding these galaxies could help scientists learn how galaxies are spread through space.

The M87 Black Hole Mass from JWST and Keck Stellar Kinematics Spanning 10 pc to 10 kpc

Emily R. Liepold, Chung-Pei Ma, Refa M. Al-Amri+1 more

AstronomerCombined JWST/NIRSpec and Keck/KCWI observations provide a contiguous 2D stellar-kinematic map of M87 over projected radii of approximately 10 pc–10 kpc, reaching about 3% of the black hole’s sphere-of-influence radius. NIRSpec spectra at R < 0.45 arcsec suffer quasiperiodic wiggle artifacts; the authors’ hyphen method predicts their wavelength-dependent frequency from detector spectral traces and fits and subtracts them exposure by exposure. Cleaned spectra show pronounced central increases in stellar velocity dispersion and h4. Triaxial Schwarzschild modeling with TriOS, using approximately 5,000 kinematic constraints in 618 spatial bins, yields a black hole mass of (5.38 ± 0.13 ± 0.22) × 10^9 solar masses. The result agrees with the earlier KCWI-only determination while reducing statistical uncertainty by a factor of 2–3; distance uncertainty now dominates. The inferred mass-to-distance ratio, GM_BH/(c²D) = 3.16 ± 0.08 microarcseconds, has a 90% credible interval overlapping the multi-epoch EHT result and offers an independent prior for future EHT analyses.

PublicResearchers combined JWST and Keck observations of stars in M87 to estimate the mass of its central black hole. After correcting repeating artifacts in the JWST spectra, they found that the spread of stellar velocities rises sharply near the center. Modeling the stars’ orbits gives a black hole mass of about 5.38 billion times the Sun’s mass, consistent with an earlier estimate using Keck data alone. The statistical uncertainty is now two to three times smaller, but uncertainty in M87’s distance remains the larger limitation. Their inferred ratio of black hole mass to distance is compatible with the Event Horizon Telescope analysis at the stated 90% credible level and could independently inform future studies.

Young explorerScientists watched how stars move near a giant black hole in a galaxy called M87. They cleaned up unwanted patterns in their telescope data, then used a computer model of the stars’ paths to work out how heavy the black hole is. Their answer is about as heavy as 5.38 billion Suns! It is still an estimate, partly because they do not know exactly how far away the galaxy is.

A pocket of oxygen in a near-pristine galaxy at z=4.2: chemical inhomogeneity at 10-parsec scales in LAP2

M. Messa, E. Vanzella, S. Rojas-Ruiz+13 more

AstronomerNew 13.6-hour JWST/NIRSpec IFU PRISM spectroscopy and archival NIRCam imaging constrain LAP2, a strongly lensed galaxy at z=4.2 behind Abell 2744 (magnification approximately 50). With M_UV=-12.7 and a stellar mass of approximately 10^5 solar masses, LAP2 comprises a compact core with an effective radius of approximately 7 pc embedded in diffuse emission with an effective radius of approximately 20 pc. Strong Hα emission, blue UV slopes, and a Balmer decrement consistent with no attenuation indicate a young burst, at most approximately 10 Myr old, with no evidence of dust attenuation. Integrated [OIII] λ5007 is undetected, giving [OIII]/Hβ≤0.61 at 3σ; an extrapolated strong-line calibration implies 12+log(O/H)≤6.4, or less than approximately 0.5% solar metallicity. A 4σ [OIII] detection in the core instead yields approximately 6.6, or approximately 1% solar. The contrast could reflect local self-enrichment, requiring approximately 0.2 solar masses of newly synthesized oxygen, or a higher core ionization parameter. The 3σ HeII λ1640 equivalent-width limit of 39 Å does not exclude a metal-free stellar contribution. LAP2 extends the spectroscopically confirmed extremely metal-poor galaxy census to star-cluster masses and M_UV≈-13. Its low-density environment supports, but does not establish, a scenario in which nearly pristine gas survives well after reionization.

PublicJWST observations reveal an exceptionally faint, small galaxy called LAP2, whose light is magnified about 50 times by the foreground galaxy cluster Abell 2744. At redshift 4.2, LAP2 has roughly 100,000 times the Sun's mass in stars, comparable to a massive star cluster, and a compact center surrounded by more diffuse emission. Its light points to a burst of star formation no more than about 10 million years old, with no evidence of dust dimming. Oxygen emission is not detected in the galaxy's combined spectrum. Using a calibration extended beyond its established range, the researchers infer an oxygen abundance corresponding to less than about 0.5% of solar metallicity, placing LAP2 among the most metal-poor galaxies known. Weak oxygen emission is detected in its center, where the inferred abundance is somewhat higher. This could mean that stars have locally added oxygen, or that the gas experiences stronger ionizing conditions. The observations do not rule out some stars containing no elements heavier than helium, but do not demonstrate their presence. LAP2's relatively empty surroundings support the idea that such environments can preserve nearly pristine gas long after cosmic reionization.

Young explorerAstronomers used the JWST telescope to study a tiny, faint galaxy called LAP2. A big group of galaxies in front of it acts like a magnifying glass, making it easier to see. LAP2 has a little bright middle with a softer glow around it. Its light suggests that it recently made young stars and has very little oxygen, though the exact amount is uncertain. Scientists found a faint sign of oxygen in the middle. Maybe stars there made some oxygen, or maybe the gas there is lit up differently. The galaxy lives in a quiet part of space, which might have helped its gas stay almost unchanged.

She Sees Shells by the Stellar Shore: A Kinematic View of NGC 253's Stellar Halo

Katya Gozman, Eric F. Bell, Richard D'Souza+4 more

AstronomerMedium-resolution Magellan/M2FS spectra of 225 stars toward NGC 253's southwestern shell yield the first resolved-star kinematic measurements for 89 stars in its halo. The authors detect kinematic substructure and identify likely accreted and in-situ regions: a low-velocity component coincident with the previously reported southwestern shell, interpreted as recently accreted debris, and an in-situ component tracing the outer disk. After subtraction of the galaxy's systemic velocity, the respective median line-of-sight velocities are -34 km/s, with uncertainties of -12/+16 km/s, and 167 km/s, with uncertainties of -14/+16 km/s. The results demonstrate the utility of stellar kinematics for distinguishing likely origins and provide a pathfinder for future work with 30 m telescopes and wide-field multiobject spectrographs.

PublicThe stars surrounding a galaxy can preserve traces of smaller galaxies it absorbed long ago. Using the Magellan telescope's M2FS instrument, researchers collected spectra of 225 stars toward a shell-shaped feature around NGC 253 and measured the motions of 89 halo stars—the first such individual-star measurements in this galaxy's halo. They found groups with different motions. One slower-moving region overlaps the known southwestern shell and is interpreted as debris from a recently absorbed companion; another component appears to consist of stars formed within NGC 253 and follows its outer disk. These origins remain interpretations of the evidence. The study shows how stellar motions can help uncover a galaxy's history and guide observations with future larger telescopes.

Young explorerA big galaxy called NGC 253 has stars scattered around its edges. Scientists studied the stars' light to learn how they move. Some stars move differently from others. The scientists think one group came from a smaller galaxy that joined the big one, while another group was born in the big galaxy itself. Watching how stars move helps scientists look for clues about a galaxy's past.

ReveaLLAGN 2: Exploring the Nuclear Gas and Stellar Kinematics of Nearby LLAGNs with JWST/NIRSpec IFU

Antoine Dumont, Nadine Neumayer, Anil C. Seth+7 more

AstronomerJWST/NIRSpec observations of eight nearby LLAGN in the ReveaLLAGN sample map stellar and gas distributions and kinematics across different Eddington ratios. All targets show slowly rotating nuclear stellar disks, with an anticorrelation between stellar line-of-sight velocity and h3, and stellar velocity dispersion increasing toward the black hole. M104 and M94 show more complex dispersion patterns, indicating multiple kinematic components. Gas rotation is frequently decoupled from stellar rotation, which the authors interpret as suggesting that the stellar gravitational potential is decoupled from the current accretion state. Gas kinematics often appear aligned with radio jets, with broader velocity dispersions along the jet direction. Line-ratio maps indicate predominantly AGN photoionisation, with shock heating becoming important only at higher Eddington ratios. Nuclear-aperture spectra reveal coronal lines in all eight sources, but spatially resolved coronal-line kinematics are obtained only in NGC5128 and NGC4395, the two highest-Eddington-ratio sources.

PublicResearchers used JWST to study the centers of eight nearby galaxies whose central black holes are weakly active. In every galaxy, the stars form a slowly rotating central disk, and the spread of stellar velocities increases toward the black hole. Two galaxies, M104 and M94, show more complicated stellar motions, indicating multiple moving components. Gas often rotates differently from the stars, and its motions frequently line up with radio jets, with a wider spread of velocities along the jets. Ratios of emission-line strengths suggest that radiation from the active galactic center mainly energizes the gas; heating by shocks becomes important only in systems feeding at higher rates relative to their Eddington limits. Emission from highly ionised gas is detected in the central spectra of all eight galaxies, but its motion can be mapped across the sky only in NGC5128 and NGC4395, the two systems with the highest relative feeding rates.

Young explorerScientists used the James Webb Space Telescope to look at the middles of eight galaxies, where giant black holes are feeding a little. They found stars slowly circling the middle in every galaxy. The gas often moves differently from the stars, and near jets it has a bigger mix of speeds. The light from around the feeding black holes seems to give the gas most of its energy. In galaxies where the black holes feed more strongly, crashing gas also seems important. Two galaxies have extra-complicated star motions, so their centers are not just simple spinning disks.

DESI DR2 Results III: The Mass of the Milky Way

DESI Collaboration, C. Aganze, J. Aguilar+97 more

• Cosmology and Nongalactic Astrophysics

AstronomerThe authors apply four dynamical methods to 10,036 RR Lyrae and blue horizontal branch stars from DESI DR2 with 6D phase-space coordinates spanning approximately 10–95 kpc from the Galactic center. Mock surveys based on cosmological simulations incorporate individual tracer stars, DESI- and Gaia DR3-like uncertainties, and survey selection functions. These tests quantify method- and tracer-dependent biases arising from modeling assumptions and galaxy disequilibrium. After mock-based bias corrections, a joint analysis accounting for residual inter-method correlations yields M(r < 80 kpc) = 6.36 (+0.53/−0.48) × 10^11 solar masses and M200c = 1.19 (+0.14/−0.12) × 10^12 solar masses. RR Lyrae-only and blue horizontal branch-only combinations give similar results. The estimates depend on dynamical modeling and simulation-based treatment of systematics, rather than constituting direct mass measurements.

PublicResearchers estimated the Milky Way’s mass by analyzing the positions and motions of 10,036 stars in its distant outer regions using DESI data. They used four methods and tested them on simulated surveys to assess and correct biases caused by modeling assumptions and departures from dynamical equilibrium. Combining the corrected estimates, they find about 636 billion solar masses within 80 kiloparsecs of the Galactic center, with a reported uncertainty of roughly 50 billion solar masses. Their estimate for the galaxy’s wider extent, expressed as its virial mass, is about 1.19 trillion solar masses, with uncertainties of +0.14 and −0.12 trillion. These are model-based estimates calibrated with simulations; analyzing the two types of stars separately gives similar answers.

Young explorerScientists wanted to find out how heavy our Milky Way galaxy is. They studied where thousands of faraway stars are and how they move. They tried four ways of working out the answer and checked them using pretend galaxies made in computers. Their best estimate is that the Milky Way has about as much mass as a trillion Suns. It is not an exact answer, but the different kinds of stars gave similar clues.

Mock catalogues for the DESI DR2 Milky Way mass modeling effort

Alexander H. Riley, Amanda Byström, Gustavo E. Medina+54 more

AstronomerThis work presents AuriDESI mock tracer catalogues generated from the Auriga cosmological simulations to support validation, in companion studies, of Milky Way mass-estimation techniques. The techniques are intended for six-dimensional kinematics of distant halo stars in a DESI DR2 Key Project. The mocks incorporate RR Lyrae and blue horizontal branch selection, line-of-sight velocity and proper-motion uncertainties, and spatially varying observational completeness within the survey footprint. The authors discuss agreement with observed DESI tracer samples and suggest improvements relevant to other mock-survey efforts; the abstract gives neither quantitative agreement metrics nor a Milky Way mass measurement. The catalogues are publicly available on Zenodo.

PublicAstronomers plan to estimate the Milky Way's mass using the positions and motions of distant stars observed by the ongoing Dark Energy Spectroscopic Instrument (DESI) survey. This paper presents simulated star catalogues designed to help test the methods used for that task. Built from the Auriga galaxy simulations, the catalogues imitate important features of the DESI sample, including which kinds of stars are selected, measurement uncertainties, and uneven coverage. The authors discuss how the simulated catalogues compare with real DESI observations and suggest ways to improve them. This is a simulation resource, not a reported measurement of our galaxy's mass, and the catalogues are freely available on Zenodo.

Young explorerScientists want to find out how much stuff is in our galaxy, the Milky Way, by studying where faraway stars are and how they move. This team made pretend star lists from computer-made galaxies so scientists can test their ways of doing that. The lists copy some of the things that make real star measurements tricky, like small mistakes and missing stars. The team discusses how the pretend lists compare with real ones and how to make them better. They have shared the lists for others to use, but this paper does not tell us how much stuff is in the Milky Way.

Constraining the Milky Way Mass profile with data driven distribution function using DESI DR2 halo stars

Yanrui Zhou, Jiaxin Han, Wenting Wang+57 more

AstronomerThe authors apply the empirical distribution function method (emPDF) to DESI Milky Way Survey halo stars to infer the Milky Way mass profile without assuming a functional form for the tracer distribution. Realistic AuriDESI mock observations are used to test and calibrate the effects of observational errors and departures from steady state. Blue horizontal branch and RR Lyrae tracers yield overall consistent halo mass profiles. Combining these stellar constraints with an independent satellite-dynamics constraint gives log(M_200c/M_sun) = 12.12 with statistical errors of -0.05/+0.05 and total errors of -0.04/+0.06, and log(c_200c) = 1.16 with statistical errors of -0.03/+0.05 and total errors of -0.07/+0.05. The corresponding mass–concentration correlation coefficients are -0.90 and -0.54. Total uncertainties include systematic errors calibrated using AuriDESI; the mocks provide calibration rather than additional observations of the Milky Way.

PublicResearchers estimated how the Milky Way's mass is distributed by modeling the motions of stars in its outer halo observed by the Dark Energy Spectroscopic Instrument. Their method does not require a preset mathematical shape for the stars' distribution. Two different kinds of stars gave broadly consistent estimates. Combining those estimates with a separate measurement based on satellite motions tightened the constraints on the halo's mass and how concentrated it is. These are model-based inferences from observations, not direct measurements of the Galaxy's weight. The team used realistic simulated observations to test and calibrate measurement errors and the effects of departures from the model's assumption that the stellar system is steady over time, and included those calibrated systematic uncertainties in the reported results.

Young explorerHow can we weigh our huge galaxy? Scientists watched how stars move around its outer parts and used a model to work out how much mass could be there. Two different kinds of stars gave answers that agreed fairly well. Adding clues from smaller galaxies moving around ours helped narrow down the answer. They also practiced with pretend observations made by a computer to check how their method could go wrong. Their answer is still an estimate, not an exact weight.

A distribution-function estimate of the Milky Way mass profile from outer halo stars in DESI DR2

Gustavo E. Medina, Thomas M. Callingham, Monica Valluri+65 more

AstronomerUsing DESI DR2 observations from its first three years, the authors estimate the Milky Way mass from 279 blue horizontal-branch (BHB) and 213 RR Lyrae (RRL) stars at approximately 50–80 kpc. Their hierarchical Bayesian Galactic Mass Estimator assumes power-law potential and tracer-density profiles and incorporates distance and velocity uncertainties. Tests on 24 AuriDESI mock catalogs reveal an approximately 15% mass overestimate at 80 kpc, which they correct. The corrected enclosed masses at 80 kpc are (0.64 ± 0.06) × 10^12 solar masses for BHBs and (0.53 ± 0.05) × 10^12 solar masses for RRLs; including Sagittarius stream stars lowers the estimates by approximately 10%. Extrapolation to 100 kpc gives 0.74 (+0.07/−0.07) and 0.62 (+0.06/−0.07) × 10^12 solar masses, respectively. Anchoring an NFW halo to the constraints at 65 kpc yields model-dependent virial masses M200 of 1.12 (+0.14/−0.12) and 0.89 (+0.11/−0.10) × 10^12 solar masses. BHBs consistently give higher masses than RRLs, highlighting sensitivity to tracer selection even within one method.

PublicAstronomers used two kinds of distant stars observed by DESI to estimate how much mass the Milky Way contains. Within 80 kiloparsecs of the Galaxy’s center, the two star samples give estimates of about 640 billion and 530 billion times the Sun’s mass, with uncertainties of about 60 billion and 50 billion solar masses. These are model-based estimates, not direct weighings: tests on simulated galaxies showed that the method tended to overestimate mass, and the researchers corrected for that bias. Including stars from the Sagittarius stream lowers the estimates by about 10%. Estimates extending farther out, including the Galaxy’s overall halo mass, require additional assumptions. The persistent difference between the two star samples shows that the choice of stars matters when weighing our Galaxy.

Young explorerHow do you weigh our giant galaxy when it cannot sit on a scale? Scientists watched two kinds of faraway stars and used their movements to work out how much stuff is in part of the Milky Way. The two groups of stars gave different answers. The scientists also tested their way of weighing with pretend galaxies made in a computer and used those tests to fix a mistake that made the answers too big. They have useful estimates, but they are still not sure of the exact weight.

Identifying Compact Object Candidates using Gaia DR3 Astrometric Accelerations and Jerks

Andrew Kinnion, Jeff J. Andrews, Eirini Kasdagli

• Solar and Stellar Astrophysics

AstronomerThis study develops a method to prioritize potential massive compact companions among Gaia DR3 sources with 9-parameter, variable-acceleration astrometric solutions. Assuming a luminous star orbiting a dark companion, the authors derive sky-projected accelerations and jerks for inclined eccentric, face-on eccentric, and face-on circular binary populations. They also construct a more realistic luminous-star–black-hole population with POSYDON. For each population, gaiamock accounts for observational selection by retaining systems assigned 9-parameter fits. The modeling indicates that joint acceleration–jerk signatures can identify promising massive-companion candidates, although these fits under-constrain complete orbits. Applications to HD 12871 and modeled Gaia BH3-like binaries illustrate the approach rather than establish new compact-object detections.

PublicA star’s changing motion across the sky may offer clues to an unseen, heavy companion. This study develops a way to search for such candidates in Gaia data, using both the star’s apparent acceleration and how that acceleration changes. The researchers model several kinds of binary systems, including stars paired with black holes, and simulate which would receive Gaia’s 9-parameter motion fits. Their modeling suggests that the two motion clues together can help select promising candidates, even when the fits cannot fully determine their orbits. They illustrate the method with HD 12871 and simulated systems resembling Gaia BH3; the abstract does not report a newly confirmed black hole.

Young explorerA star can move in a curved path if it has an unseen partner. Scientists made computer models to learn which changes in a star’s motion might hint at a heavy, dark partner, such as a black hole. They hope to use these clues in Gaia’s star measurements. The clues could help choose stars to study, but they do not prove a black hole is there.

Revisiting the Stellar-Dynamical Mass of the Central Black Hole in NGC 3227

Nabanita Das, Misty C. Bentz, Eugene Vasiliev+2 more

AstronomerThe authors infer a stellar-dynamical black hole mass of (1.2 ± 0.5) × 10^7 solar masses for the nearby Seyfert galaxy NGC 3227. They derive nuclear stellar line-of-sight velocity distributions from archival spatially resolved Gemini/NIFS K-band spectra, represent the surface brightness with four components measured from an HST/WFC3 F547M image, and fit Schwarzschild orbit-superposition models using FORSTAND. Higher signal-to-noise spectra constrain higher-order LOSVD moments, yielding a more precise mass than the earlier orbit-based stellar-dynamical estimate by Davies et al., with which it agrees. The result also agrees with the velocity-resolved reverberation-mapping constraint from Bentz et al. It is slightly below the gas-dynamical constraint from Hicks and Malkan after scaling to the same adopted distance, but the two are consistent within 2σ. Such cross-method comparisons help assess mass-scale consistency, uncertainties, and potential biases.

PublicResearchers used observations of stars moving near the center of the nearby galaxy NGC 3227 to estimate its central black hole's mass. By fitting models of stellar orbits to archival infrared spectra and a Hubble image of the galaxy's light, they inferred a mass of about 12 million times the Sun's mass, with a quoted uncertainty of 5 million solar masses. The improved quality of the stellar spectra makes this estimate more precise than an earlier stellar-motion measurement, while remaining consistent with it. It also agrees with an estimate from reverberation mapping, a different technique. A previous estimate based on gas motion is somewhat higher, but the difference is within twice the quoted statistical uncertainty. Comparing these methods helps researchers check whether black hole mass estimates share a consistent scale and identify possible biases.

Young explorerA nearby galaxy called NGC 3227 has a huge black hole in its middle. Scientists studied how stars move near it and used computer models of their paths to work out how massive the black hole might be. Their best estimate is about as much mass as 12 million Suns, but the answer is not exact. It agrees with some earlier estimates. Another estimate made using moving gas is a little bigger, but the scientists cannot say the two clearly disagree. Checking different ways of measuring helps them see how well those ways work.

The impact of Population III stars on the elemental enrichment of ultra-faint galaxies in the FIRE-3 zoom-in simulations

Pratik J. Gandhi, Earl P. Bellinger, Marla Geha+7 more

AstronomerThe observed Local Group ultra-faint galaxy stellar mass–metallicity relation remains difficult to reproduce theoretically. The authors explore Population III enrichment and feedback using FIRE-3 cosmological baryonic zoom-in simulations of isolated ultra-faints evolved to z=0 and LMC-mass environments. Their sub-grid prescriptions assign stars forming below a critical metallicity an IMF restricted to 8–100 solar masses. These variants produce effective z=0 metallicity floors of roughly 10^-5–10^-3 solar metallicity, or [Fe/H] ≈ -7 to -5, depending on the model. However, Pop. III inclusion does not systematically bring all or even most simulated ultra-faints to [Fe/H] ≈ -2.5, although some reach that level. Those that do have extended star formation after Pop. III enrichment and substantial iron contributions from Type Ia supernovae, indicating that Pop. III iron enrichment alone is insufficient. The study also examines metallicity distributions and [Mg/Fe] and predicts a stellar mass–[Mg/H] relation from the simulations.

PublicObservations show that ultra-faint galaxies in the Local Group contain amounts of heavy elements that many theories struggle to explain. This study tests whether enrichment by the first generation of stars could help, using computer simulations with different prescriptions for these stars. The models assume that this early population contains only massive stars. Their enrichment establishes a minimum heavy-element content in the simulated galaxies, but it does not reliably raise their iron content to the observed level. Some simulated galaxies do reach that level; these continue forming stars after the first stars enrich their gas and receive substantial additional iron from explosions of white dwarfs, called Type Ia supernovae. The results therefore suggest that the first stars alone cannot supply enough iron. The authors also use their simulations to predict how magnesium abundance varies with galaxy stellar mass; this is a prediction, not a new observational finding.

Young explorerTiny galaxies have stars with iron and other ingredients inside them. Scientists used computer pretend-galaxies to test whether the very first stars could supply enough of those ingredients. In their models, the first stars helped, but usually did not provide enough iron to match what astronomers see. Some pretend-galaxies got enough when they kept making stars and later explosions of white dwarf stars added more iron. This suggests that the first stars needed help from later stars.

Mock CSST NUV-NIR imaging of TNG50 galaxies with resolved stellar populations

Jing Tang, Ran Li, Yang Chen+5 more

AstronomerThe authors present a framework for generating CSST-like mock images of resolved stellar populations, demonstrated on a spiral and a dwarf irregular galaxy from TNG50 in seven photometric bands. TRILEGAL samples individual stars from simulation star particles; bright stars are retained explicitly, while fainter stellar light and nebular emission form a diffuse component. A SKIRT dust model, based on gas mass and metallicity, supplies line-of-sight extinction for individual stars and radiative-transfer transmission maps for diffuse light, with additional birth-cloud attenuation for embedded young stars. The CSST simulation pipeline adds PSF convolution, sky background, and instrumental noise. These are simulated images, not observations. With known astrometric and photometric calibration information, they are intended as inputs for subsequent source detection, photometric recovery, and completeness analyses; results from those analyses are not reported. The framework is designed for adaptation to other hydrodynamic simulations and observing configurations.

PublicThis study creates simulated images showing how individual stars and the surrounding glow in computer-model galaxies might appear in CSST observations. The authors demonstrate their method using two simulated galaxies: a spiral galaxy and a dwarf irregular galaxy, each imaged in seven bands. They model bright stars individually and combine fainter stars and emission from star-forming regions into a diffuse glow. They also account for dust dimming the light, including extra dimming around young stars still inside their birth clouds, and add expected image blurring, sky background, and instrument noise. The images are not real observations. They are intended to help later studies test how well stars can be found and their brightness measured, and how many stars may be missed. The method is designed to be adaptable to other galaxy simulations and observing setups.

Young explorerThe researchers made pretend space pictures from two galaxies inside a computer. They put in bright stars, a soft glow from fainter stars and glowing gas, and dust that hides some of the light. They also made the pictures blurry and noisy, like pictures taken by a telescope. These are not pictures of real galaxies in the sky. They are made to help researchers later test how well they can find and measure stars.

Spectroscopy-informed Deep Learning Searches for Photometric Little Red Dots in JWST Surveys

Chenxuan Zhang, Huanian Zhang, Qingwen Wu

AstronomerLittle Red Dots (LRDs) are compact, red, high-redshift sources discovered with JWST, characterized by V-shaped spectral energy distributions (SEDs). This study develops a cross-modal machine-learning framework using matched NIRCam imaging and NIRSpec/PRISM spectroscopy to enable spectroscopy-informed classification from NIRCam imaging alone. Among spectroscopically observed high-redshift galaxies previously classified as non-LRDs, the model selects 35 new LRD candidates. Most satisfy at least one independent LRD color criterion; of the 13 with medium- or high-resolution NIRSpec grating spectra, 10 show broad H-alpha emission, a hallmark of LRDs. Application to public Dawn JWST Archive imaging and two independent JWST surveys yields 357 and 23 additional candidates, respectively. The recovered candidates span broader observed SED properties than existing samples, suggesting that color-based selections may miss part of the diversity of LRD-like systems. These selections remain candidates rather than uniformly confirmed LRDs.

PublicLittle Red Dots are compact, reddish sources seen by the James Webb Space Telescope in the distant universe. Astronomers usually identify them using color rules, but different rules can select different populations. This study trains a machine-learning system with both telescope images and spectra, which separate light by wavelength, so it can search for candidates using images alone. It flags 35 candidates among galaxies previously classified as not being Little Red Dots. Most meet at least one separate color-based test. Of 13 with more detailed spectra available, 10 show broad emission from hydrogen, a characteristic feature of Little Red Dots. Searches of additional public images produce another 357 candidates from one archive and 23 from two other surveys. Their more varied light patterns suggest that existing color rules may overlook some Little Red Dot-like sources, although the new selections are not all confirmed.

Young explorerThe Webb telescope has found tiny-looking red dots very far away in space. Scientists often pick them out by their colors, but that might leave some out. In this study, scientists taught a computer using pictures and light split into different colors. Then the computer searched pictures for more possible Little Red Dots. It found hundreds of candidates, but they are not all confirmed. Some had a special sign in their light that helped support the computer's choices. The study suggests these dots may have more varied light patterns than the usual color rules can find.

Aperture-dependent [O III] profile variability: Clues to the nature of double-peaked narrow emission lines

Qi Zheng, Xingqian Chen, Zhegeng Chen+2 more

AstronomerThe authors propose using aperture-dependent changes in double-peaked narrow emission lines to constrain narrow-line region (NLR) kinematics and their physical origin. Comparing SDSS, DESI, and LAMOST spectra of SDSS J0941, they find significant profile differences, showing that aperture effects strongly influence the integrated lines. A two-nucleus AGN geometry perpendicular to the line of sight can qualitatively explain asymmetric sampling but not the differing peak separations. The asymmetric changes also disfavor a simple AGN-driven outflow and a rotating disk-like NLR. Among the models considered, only a more complex, non-axisymmetric rotating NLR gives a self-consistent explanation: a compact blueshifted region remains largely within the smaller aperture, with increased line width and little flux change, while a more extended redshifted region loses both flux and line width. This is a favored interpretation rather than a unique determination; the study highlights both the diagnostic value of multi-aperture spectroscopy and the difficulty of distinguishing physical scenarios.

PublicThe researchers propose a way to investigate why some gas emission lines have two peaks: compare spectra collected through openings that include different amounts of the emitting region. They tested this approach on SDSS J0941 using spectra from three surveys and found substantial differences in the shapes of its double-peaked lines. Those differences show that how much of the region is included can strongly affect the measured spectrum. Among the explanations they considered, a complex, unevenly distributed rotating gas region best accounts for the changes. In this interpretation, the gas producing the blueshifted peak is more compact, while the gas producing the redshifted peak is more spread out and more strongly excluded by a smaller opening. Simpler outflow and rotating-disk explanations are disfavored, and a two-nucleus model cannot explain all the differences. The comparison offers useful clues, but does not uniquely establish the gas arrangement.

Young explorerScientists studied light from glowing gas that makes two bumps in a special light chart. They compared views through different-sized openings, a bit like looking through big and small windows. The bumps changed when different amounts of gas were included. Of the ideas they tried, swirling gas spread out unevenly explained the changes best: one part may be packed close together, while another is more spread out. That is an explanation that fits the clues, not something they know for sure.

Evolutionary Map of the Universe (EMU): Selection of active galactic nuclei and star-formation emission with machine-learning techniques

R. Carvajal, I. Matute, J. Afonso+13 more

AstronomerA pre-trained, multi-stage ML pipeline applied to optical-to-infrared photometry classifies EMU pilot-survey sources as AGN- or non-AGN-dominated and estimates photometric redshifts, enabling derived radio luminosities. EMU-PS covers 270 deg2 at 944 MHz with rms approximately 30 microJy/beam. The authors report increasing known AGNs by more than 15-fold, with 96% recall, out to z approximately 5, and non-AGNs by nearly 100-fold, with 94% recall, at z > 1. A non-negligible low-redshift subset labelled non-AGN has radio luminosities exceeding expectations from star formation alone, demonstrating that photometric and radio classifications need not agree. Radio properties show expected luminosity trends and no detected evolution of in-band spectral indices over 800–1088 MHz. Extrapolation to the full EMU survey predicts more than 3.4 million AGN candidates, rather than confirmed detections. The pipeline offers a scalable catalogue-building approach, with multi-wavelength analysis revealing populations and trends that colour cuts or spectroscopy alone can miss.

PublicResearchers used a trained machine-learning system to sort radio sources in the EMU pilot survey into those dominated by active galactic nuclei and those attributed to other processes, including star formation. Using optical and infrared measurements, the system also estimated redshifts, which helped the team calculate radio luminosities. The work greatly expanded the catalogue of classified sources. However, some nearby sources labelled as non-active had stronger radio emission than star formation alone would explain, showing that classifications based on different kinds of light can disagree. The team found expected luminosity trends and no detected change with redshift in how radio emission varies across the survey’s frequency band. They predict that applying the method to the full EMU survey could identify more than 3.4 million active-galaxy candidates; this is an extrapolation, not a count already observed.

Young explorerScientists used a computer helper to sort things seen in a radio map of the sky. It used other kinds of light to guess whether the radio glow mostly came from a galaxy’s active middle or from things like making stars. It helped label many more sources. But some labels did not match what the radio glow suggested, so the answers need care. The scientists think a much bigger survey could find millions of possible active galaxies, but they have not found all of those yet.

A brief overview of the baryon cycle in galaxies

S. Veronese

AstronomerThis brief review surveys the baryon cycle linking the cosmic web, circumgalactic medium (CGM), and interstellar medium (ISM). It covers gas accretion onto galaxies, conversion of gas into stars, and feedback processes that regulate galaxy growth. The abstract reports no specific new measurements or simulation results; it highlights unresolved questions to motivate further cosmological simulations, multiwavelength observations, and theoretical work.

PublicGalaxies form and change through an ongoing exchange of gas with their surroundings. This review brings together current understanding of how gas enters galaxies, becomes stars, and is affected by processes that regulate galaxy growth. Rather than announcing a new discovery, it points to unanswered questions that future observations, computer simulations, and theory could help resolve.

Young explorerGalaxies are huge groups of stars with gas around and inside them. Gas can move into galaxies and become new stars, while other processes help control how galaxies grow. This paper explains what scientists understand about that cycle and points out questions they still need to answer.

Quiescent galaxies at cosmic noon: from individual element abundances to star formation histories

M. Longhetti, F.R. Ditrani, D. Bevacqua+10 more

• Instrumentation and Methods for Astrophysics

AstronomerThis science case proposes measuring full elemental abundance patterns in a representative sample of massive quiescent galaxies at z ~ 2–3 using rest-frame optical absorption features. Such measurements could constrain star-formation and assembly histories, extending chemical studies that remain very limited at these redshifts. The authors argue that robust stellar-population constraints require S/N ~ 20 per resolution element and spatial resolution comparable to the galaxies’ ~ 0.1 arcsec sizes, necessitating a 40m-class telescope with powerful adaptive optics. Within this assessment, they identify SHARP-NEXUS with MORFEO-MCAO as the only viable ELT instrument for the task. To use multiplexing efficiently despite the rarity of these galaxies, they propose targeting overdensities and sharing observations with surveys of star-forming galaxies. The abstract presents observational requirements and a strategy, not new abundance measurements.

PublicThe chemical makeup of stars can help reveal how galaxies formed and how quickly they built their stars. This paper proposes studying massive galaxies that have largely stopped forming stars at an epoch called cosmic noon, corresponding to redshifts of about 2–3. These galaxies are faint and appear very small, making detailed chemical measurements difficult. The authors argue that the work needs a telescope in the 40-metre class with a system that corrects atmospheric blurring, and identify SHARP-NEXUS combined with MORFEO-MCAO as the only viable ELT instrument for their proposed study. They suggest observing regions where galaxies are concentrated and coordinating with other galaxy surveys to make efficient use of the instrument. This is a plan for future measurements, not a report of newly measured chemical abundances.

Young explorerScientists want to learn how some big, faraway groups of stars grew long ago. These galaxies have mostly stopped making new stars. Looking closely at their light could give clues about what they are made of and how they grew. But they look very faint and tiny, so the scientists say they need a huge telescope with special tools to make the view sharper. This paper explains their plan; it does not yet tell us what they found inside those galaxies.

Understanding galaxies and the origin of the golden mass through the study of scaling relations across cosmic history

C. Tortora, A. Gallazzi, A. Gargiulo+4 more

AstronomerThis white paper proposes using SHARP on the ELT to investigate the emergence of the galaxy “golden mass.” The abstract identifies a characteristic stellar mass of 5 × 10^10 solar masses where star formation efficiency peaks and feedback has minimal influence on star formation; stellar-mass relations involving stellar population gradients, dark matter fractions, and total mass density slopes also show pronounced minima near this scale. Its origin and evolution remain uncertain, particularly at the largely unexplored epochs z > 1.5. The proposed mIFU observations would provide spatially resolved stellar population and dynamical maps of early- and late-type galaxies, enabling measurements of these quantities across cosmic time. Comparisons with cosmological simulations would help assess the roles of mergers, supernova feedback, and active galactic nucleus feedback. These are prospective capabilities and scientific goals, not new observational results.

PublicGalaxies appear to have a characteristic stellar mass—about 50 billion times the Sun’s mass—at which they turn gas into stars most efficiently. Other relationships involving their stars, dark matter, and mass distribution also show distinctive dips around this “golden mass.” Why this scale exists, and when it emerged, remain open questions. This white paper proposes studying galaxies at early cosmic times with SHARP, an instrument planned for the Extremely Large Telescope. Its proposed observations would map stellar populations and motions within galaxies to investigate their mass distributions. Comparing those observations with computer simulations could help researchers understand how galaxy mergers and feedback from supernovae and active galactic nuclei shape this pattern. The paper presents a research plan rather than new measurements.

Young explorerGalaxies are huge groups of stars with gas that can make more stars. Scientists have noticed that galaxies with a certain amount of stars seem especially good at turning gas into new stars. They call this the “golden mass,” but they do not yet know why it happens or when it began. This paper describes a plan to use a telescope tool called SHARP to look at galaxies as they were long ago. Scientists hope those views, compared with computer models, will help solve the puzzle. They have not made these new observations yet.

Supermassive black holes and nuclear star clusters in galaxies: constraining formation and co-evolution with SHARP and MICADO

E. Dalla Bonta', E. Portaluri, C. Arcidiacono+7 more

AstronomerThis paper outlines a framework for testing the formation and coupled evolution of nuclear star clusters and supermassive black holes using near-infrared integral-field spectroscopy with SHARP on the Extremely Large Telescope and high-resolution MICADO imaging. Joint modelling of stellar dynamics, populations, and nuclear structure is intended to constrain black-hole masses, cluster internal kinematics, and gas-inflow signatures in the same systems, while establishing the mass and distance regimes where constraints are robust. The key questions concern cluster assembly, black-hole dynamical dominance, and the suppression, destruction, or replacement of compact stellar nuclei by cusp-like structures. The abstract reports no new quantitative measurements. Recent discoveries of compact active nuclei at high redshift indicate efficient black-hole growth in systems with weak or compact stellar components, but nearby galaxies are explicitly not treated as evolutionary analogues; their nuclear diversity instead offers a laboratory for isolating relevant physical mechanisms.

PublicGalaxy centres can contain both a dense cluster of stars and a supermassive black hole. How these components form, grow together, or come to dominate one another remains uncertain. This paper describes how two instruments on the Extremely Large Telescope, SHARP and MICADO, could combine infrared spectroscopy and detailed images to test competing explanations. The approach is designed to measure black-hole masses, stellar motions inside central clusters, and signs of gas flowing inward, while determining which galaxies can yield reliable measurements. These are proposed capabilities rather than new measurement results reported in the abstract. Discoveries of compact active centres in the distant, early universe indicate that black holes can grow efficiently even where stellar components are weak or compact. Nearby galaxies are not direct stand-ins for those early systems, but their varied centres could help reveal the processes involved.

Young explorerSome galaxies have a tightly packed bunch of stars and a huge black hole in their middle. Scientists still want to know how they grow and change together. This paper describes a plan to use two telescope tools to study the stars’ light, how they move, and clues that gas is flowing inward. It does not report new measurements from that plan. Scientists have already found clues that black holes in the early universe could grow well even with only a small or tightly packed group of stars around them. Galaxies nearby are not copies of those early galaxies, but studying them could help scientists understand what happens in galaxy middles.

Net Cooling Tables for Cosmological Simulations under Multiple UV/X-ray Background Models

Laura Di Federico, Klaus Dolag, Ildar Khabibullin+3 more

AstronomerThe authors present three sets of element-by-element cooling tables calculated with CLOUDY 23.01 for optically thin gas in photoionization equilibrium under three UV/X-ray backgrounds. Compatible with existing tables, they separately tabulate cooling, heating, and net rates for hydrogen and helium across an extended range of helium mass fractions and for 13 heavy elements, alongside hydrogen species fractions, electron abundances, and mean particle masses. For Solar-composition gas, background choice has little effect on net cooling at low redshift, but differences grow at high redshift, especially for diffuse gas near thermal equilibrium. Relative to widely used previous tables, cooling times in this regime differ by up to a factor of ten at z ≳ 4.6; at z ≈ 8, the calculations disagree on the sign of net energy exchange across nearly 10% of the diffuse density-temperature plane relevant to the intergalactic medium. These trends also occur in hydrogen-and-helium-only gas. These are calculated differences, not observational measurements; the tables provide a framework for testing radiation-background effects in cosmological hydrodynamical simulations.

PublicHow gas gains and loses heat is an important ingredient in computer simulations of the universe. This study supplies three sets of calculated reference tables, each using a different model of the ultraviolet and X-ray radiation that bathes cosmic gas. The calculations assume gas is transparent to this radiation and that its ionization state is in equilibrium with it. For gas with the Sun’s chemical composition, the radiation model makes little difference to net cooling in the relatively recent universe, but much larger differences arise at earlier times, especially in thin gas whose heating and cooling nearly balance. Compared with widely used older tables, calculated cooling times can differ by as much as a factor of ten at redshifts of about 4.6 and above. At a redshift of about 8, the calculations even disagree about whether gas heats or cools across nearly 10% of the thin-gas density and temperature conditions considered. Similar trends appear for gas containing only hydrogen and helium. These are theoretical calculations intended to help assess simulation uncertainties, not direct observations of gas temperatures.

Young explorerScientists made new computer tables to work out when gas in space warms up or cools down. They tried three different ideas about the light shining through space. For the more recent universe, the answers were much alike. For the very early universe, some answers were very different: sometimes one calculation said the gas would warm up while another said it would cool down. The scientists did not watch this happen in space. Their tables will help people explore how these different ideas about light change their computer models of the universe.

AGN Host Galaxies in COSMOS-Web: Linking Structural Evolution and Star Formation Quenching up to z=5

Xiao Han, Lilan Yang, T. Kelly+20 more

AstronomerUsing high-resolution COSMOS-Web JWST imaging and archival multiwavelength photometry, the study compares the rest-frame optical size–mass distribution of 3,955 AGN hosts selected through five diagnostics at 0<z<5 with those of star-forming and quiescent galaxies. At z≳2, massive hosts (M⋆>10^10.5 solar masses) generally have star-forming-galaxy-like sizes despite suppressed star formation. At lower redshift, massive hosts lie increasingly near the quiescent size–mass relation, with lower specific star formation rates and higher Sérsic indices; lower-mass hosts remain near the star-forming relation. Overall size evolution is mild, Re∝(1+z)^−0.6 over 0<z<4, shallower than for typical star-forming and quiescent galaxies. In the star-formation-offset versus compactness-offset plane, hosts at z<2.2 predominantly occupy compact star-forming and quiescent regions, broadly consistent with compaction followed by quenching. Some hosts at z>2.2 instead have suppressed star formation while remaining relatively extended. These observations suggest that suppression may precede substantial compaction in some hosts, but do not establish that AGN activity causes the suppression.

PublicThe researchers studied 3,955 galaxies with active galactic nuclei, using sharp JWST images and other observations to compare their sizes, stellar masses, and star formation with those of star-forming and quiet galaxies. The pattern depends on both mass and cosmic era. In the earlier universe, massive galaxies with active nuclei often had reduced star formation but were still about as large as ordinary star-forming galaxies of similar mass. At later times, massive hosts increasingly resembled quiet galaxies in size and had more centrally concentrated light, while lower-mass hosts remained closer to star-forming galaxies. The findings suggest that some galaxies may slow their star formation before becoming substantially more compact, rather than always becoming compact first. They do not settle whether activity in the nucleus is responsible for shutting down star formation.

Young explorerGalaxies are huge groups of stars. Scientists looked at many galaxies with very bright, active centers to see how big they were and how many new stars they were making. Some galaxies seen long ago were making fewer new stars but were still spread out. That is a clue that some galaxies may slow down their star-making before becoming more tightly packed. It does not prove that their busy centers made them slow down.

Gaia DR3 Reveals the Kinematics of Young Stellar Objects in the Carina Nebula: Peripheral Expansion and Central Rotation

Xinyu Yang, Yuxin He, Chaojie Hao+10 more

AstronomerThe study combines a young stellar object sample cross-matched with Gaia DR3, 12CO (1–0) molecular-gas observations, and APOGEE radial velocities to investigate Carina’s kinematics. YSO proper motions show systematic outward expansion in four peripheral subregions, with two-dimensional expansion velocities of approximately 0.57–4.56 km/s. Central Region YSOs exhibit ordered rotation about an axis at position angle 86.9 ± 1.5 degrees, with a rotation velocity of 1.75 ± 0.03 km/s. Momentum estimates suggest that the peripheral expansion may reflect combined feedback from massive OB stars and possible past supernovae. The authors interpret these findings as evidence that massive-star feedback dominates the cloud’s dynamical evolution; the proposed contributions to the expansion are not established directly.

PublicResearchers combined measurements of young stars’ motions with observations of molecular gas to study how the Carina Nebula is moving. Young stars in four outer areas show a consistent outward expansion, with speeds across the sky of about 0.57–4.56 kilometres per second. Young stars in the central area show an organized rotation at 1.75 ± 0.03 kilometres per second. Estimates of momentum suggest that the outer expansion may be driven jointly by the influence of massive stars and possible past stellar explosions. The authors conclude that massive stars strongly shape the cloud’s motion, although the specific causes of the expansion remain an interpretation rather than a directly established result.

Young explorerScientists watched how young stars move in a big space cloud called the Carina Nebula. In four outer parts, the young stars are spreading outward. Near the middle, young stars move in an orderly turning pattern. The scientists think big stars may help push the outer parts outward, and stars that might have exploded long ago could have helped too. They found the motions, but they are not certain exactly what caused the spreading.

Primary and Secondary Star Formation in the Spiral Waves of NGC 628

Bruce G. Elmegreen, Sean T. Linden, Kelsey E. Johnson+11 more

AstronomerThe study compares optically identified and embedded or emerging young star clusters (eYSCs) in NGC 628. The youngest clusters extend farther into spiral arms at small radii than at large radii, consistent with faster angular flow through a wave-like arm farther from corotation. Using 7.7-micron morphology, the authors associate eYSCs with arm filaments, spurs, interarm feathers, and bubbles. They interpret arm-related eYSCs as a first generation formed by density-wave compression and bubble-rim eYSCs as secondary generations formed by feedback compression. Filament-associated eYSCs reach significantly higher masses than bubble-associated eYSCs; the latter contribute approximately one-third of the total emerging-cluster mass. The authors interpret continued secondary formation downstream as erasing the expected cross-arm age gradient. The greater mixing of arm- and bubble-related eYSCs in the outer arms is proposed as a diagnostic of wave versus material arms and of corotation in wave-like arms. Eight of the 17 most massive clusters, with log M(Msun)>4, form four tight pairs; at least one pair has a dynamical time comparable to its cluster ages.

PublicA study of star clusters in the spiral galaxy NGC 628 explores how spiral arms and the effects of existing stars may help new stars form. The youngest clusters reach farther into the arms in the galaxy’s inner regions than in its outer regions, a pattern consistent with gas moving through wave-like spiral arms. The researchers interpret clusters associated with the arms as forming when a spiral wave compresses gas, and clusters around bubble edges as later generations triggered by compression from stellar feedback. Clusters in arm filaments reach higher masses than those around bubbles, but bubble-associated clusters still account for about one-third of the mass in emerging clusters. Continued formation of these later generations could explain why the expected progression of cluster ages across the arms is absent. The more mixed arrangement of arm- and bubble-associated clusters farther out may help distinguish different kinds of spiral arms and locate where stars and an arm pattern rotate together. The study also finds four close pairs among the 17 most massive clusters.

Young explorerIn a galaxy called NGC 628, astronomers studied groups of young stars. Some are along the galaxy’s spiral arms, and others sit around the edges of bubbles. The astronomers think the arms squeeze gas to make stars, and that stars can help squeeze more gas around bubbles to make new groups. The star groups in thin strands along the arms can be bigger than those around bubbles. But the bubble groups are important too: they hold about one-third of the mass in the groups still coming out of their birth clouds.

The dwarf galaxy NGC 185: the flagship of Andromeda's dwarf galaxies for the study of evolved multiple stellar populations

Paolo Ventura, Chiara Ventura, Richard D'Souza+6 more

AstronomerUsing NGC 185 as a test case, the study assesses evolved-star diagnostics for reconstructing dwarf elliptical galaxy star formation histories where the main-sequence turn-off is too faint, motivated by HST and JWST studies at 10–15 Mpc. Population synthesis simulations based on low- and intermediate-mass stellar evolution models reproduce the stellar colour distribution and luminosity function in the F606W–F814W versus F814W diagram. Horizontal branch modelling constrains ancient star formation, reddening, distance and RGB mass loss; the red clump luminosity function constrains star formation within the past 8 Gyr. The inferred values are E(B−V)=0.20 mag, DM=24.10 mag and mean RGB mass loss of 0.22 ± 0.01 solar masses. The reconstructed history places half the stars at ages greater than 11 Gyr. HB morphology indicates essentially no metallicity spread among stars older than 8 Gyr, while the RGB slope suggests slight metal enrichment in some stars younger than 5–6 Gyr. The proposed extension to more distant dwarf ellipticals depends on adequately constraining RGB mass loss and remains subject to uncertainties in stellar evolution models.

PublicThe researchers tested whether bright, evolved stars can reveal a galaxy’s history when the faint stars normally used for this purpose are too difficult to study. They compared the colours and brightnesses of stars in the dwarf elliptical galaxy NGC 185 with simulated stellar populations. Their reconstruction suggests that half its stars formed more than 11 billion years ago. The models also indicate little variation in metal content among its oldest stars, with signs of slight enrichment in some younger stars. The analysis estimates the galaxy’s distance, the reddening caused by dust and how much mass stars lose during their red giant phase. This approach could help reconstruct the histories of more distant galaxies, but its reliability depends on understanding stellar mass loss and resolving remaining uncertainties in the models.

Young explorerA galaxy is a huge group of stars. Scientists wanted to learn when the stars in a galaxy called NGC 185 were born. They compared the colours and brightnesses of some bright, older stars with computer-made groups of stars. Their best match suggests that half the galaxy’s stars were born more than 11 billion years ago. This could help scientists learn about galaxies farther away, too. But they still need to understand better how stars change and lose some of their material as they grow old.

Living near filaments: How environment shapes age profiles in low-mass galaxies

Elisa A. Tau, Diego Pallero, Rory Smith+3 more

AstronomerMotivated by recent reports of U-shaped radial stellar-age profiles in low-mass galaxies, this study examines their environments in the IllustrisTNG-50 hydrodynamical simulation. The sample spans stellar masses of 10^9–10^10 solar masses. A U-shaped profile requires stellar ages to decline toward a local minimum and then rise, with an age contrast of at least 0.4 Gyr on each side. The authors identify 145 such galaxies, approximately 11% of the sample; about 72% are centrals and 82% inhabit halos with M200 below 10^12 solar masses. These simulated galaxies lie far from galaxy groups but relatively close to cosmic filaments: their median filament distance is about 265 kpc, compared with 351 kpc for galaxies without U-shaped profiles. The findings characterize an environmental association in the simulation, rather than establishing a causal origin for the profiles.

PublicSome low-mass galaxies have a distinctive pattern in their stars’ ages: moving outward from the center, the stars become younger and then older again. This differs from the more usual pattern in low-mass galaxies, where stellar ages increase outward. To investigate where galaxies with this U-shaped pattern tend to live, researchers studied a computer simulation, not a new set of observations. Among simulated galaxies with one billion to ten billion solar masses in stars, they found 145 with the pattern, about 11% of the sample. Most were central galaxies in their halos, and about 82% occupied halos below one trillion solar masses. They were far from galaxy groups but closer to the cosmic web’s filaments than galaxies without the pattern: typical distances were about 265 versus 351 kiloparsecs. These results identify a connection with surroundings in the simulation, but do not show that filaments cause the age pattern.

Young explorerA galaxy is a huge collection of stars. In some galaxies, the stars are older near the middle, younger farther out, and older again near the outside. Scientists used a computer-made universe to look for galaxies with this pattern. They found that these galaxies tended to be far from groups of galaxies but closer to long strands of the cosmic web than galaxies without the pattern. This is a clue from a simulation, not proof that the strands made the stars arrange their ages this way.

Investigating the initial conditions of globular clusters via N-body simulations: I. half-mass radius and stellar density

Ruoyun Huang, Baitian Tang, Long Wang+5 more

AstronomerThe authors model the long-term dynamical evolution of the low-mass outer-halo globular clusters Eridanus and Whiting 1 with the direct N-body code PeTar. Matching simulated stellar number-density profiles to observations yields best-fit initial half-mass radii of 2.0 ± 1.0 pc and 2.5 ± 0.5 pc, respectively. The corresponding inferred initial surface densities are 2592.03 and 226.35 solar masses per square parsec, 2–3 orders of magnitude above present-day values. These model-based reconstructions attribute the clusters’ diffuse present states to dynamical expansion and tidal stripping. The contrast between multiple-population-hosting Eridanus and the absence of multiple populations in Whiting 1 and young massive clusters supports, but does not establish, a requirement for higher initial surface density and/or lower metallicity in multiple-population formation. Using the simulations as a template, the authors also identify five high-probability extra-tidal candidates associated with Whiting 1 in Gaia DR3 and APOGEE DR17, with coherent kinematics and chemical abundances; their association remains a candidate identification.

PublicTwo loose collections of stars far out in our galaxy may have begun much more tightly packed. Researchers simulated the evolution of the globular clusters Eridanus and Whiting 1 and compared the models with their observed stellar distributions. The best-fitting models imply that their initial surface densities were roughly 100–1,000 times greater than today, with gradual expansion and the stripping of stars by gravitational tides producing their current diffuse appearance. Differences in whether these clusters contain distinct stellar populations support the idea that forming such populations requires denser starting conditions and/or a lower abundance of elements heavier than helium, but do not prove it. Guided by the simulations, the team also found five stars beyond Whiting 1’s tidal boundary whose motions and chemical makeup make them promising, not confirmed, associated stars.

Young explorerTwo big groups of stars look spread out today. Scientists made computer models to explore how they got that way. The models suggest the stars started much closer together, then spread apart as some stars were pulled away. The scientists also found five stars outside one group that might belong with it, but they are not sure yet.

Euclid Quick Data Release (Q1). Refining the strong lens sample with Space Warps crowd-sourced science

Euclid Collaboration, P. Holloway, A. Verma+97 more

AstronomerThis study tests citizen-scientist refinement of strong gravitational lens candidate samples using four grades: definite, probable, possible, and non-lens. Volunteers can correctly identify examples of each grade, and their responses can be calibrated to match researcher grading. Grade posteriors converge fastest for non-lenses; the reported comparison finds one researcher classification equivalent to 1.9 volunteer classifications. Both groups show substantial disagreement on intermediate-grade candidates, motivating calibrated lens probabilities to account for grading subjectivity. In a hypothetical rerun of the Q1 search with calibrated volunteer grading, the authors estimate 79% completeness for definite and probable lenses at 41% purity before researcher inspection, corresponding to an expected 12,500 true lenses in Euclid DR1. These are conditional performance and yield estimates, not an observed lens count.

PublicCitizen scientists can help researchers sort possible strong gravitational lenses into more useful categories than simply lens or non-lens. The study finds that volunteers can recognize definite, probable, possible, and non-lens examples, and that their judgments can be adjusted to be comparable to researchers’ judgments. Clear non-lenses are classified most quickly, while both volunteers and experts often disagree about less certain candidates. The authors suggest using calibrated probabilities to reflect that uncertainty. They estimate that rerunning the Q1 search with calibrated volunteer grading could recover 79% of definite and probable lenses, although only 41% of the selected sample would be genuine lenses before expert review. The associated forecast of 12,500 true lenses in Euclid DR1 is conditional, not a count already established.

Young explorerVolunteers helped scientists sort pictures that might show a space lens into four groups: yes, probably, maybe, and no. The study found that volunteers could recognize examples in every group, and their answers could be adjusted to compare with scientists’ answers. Both volunteers and scientists sometimes disagreed about the tricky pictures. The researchers think this teamwork could help find many more space lenses, but that is an estimate, not something they have already done.

Magnetic Properties of Galactic Molecular Clouds

Philip C. Myers, Ian W. Stephens, Simon Coudé+2 more

AstronomerRecent CO surveys find molecular-cloud mass–radius slopes 2 < s < 3, compared with the classical third Larson relation s ≈ 2. The authors show that virial-equilibrium equations for pressure-confined, magnetically subcritical clouds accommodate these slopes, unlike the critical, supercritical, or nonmagnetic cases considered. Fits to CO survey trends for approximately 1,500 clouds have correlation coefficients of 0.8–1 and imply median inner-Milky-Way values λ ≈ 0.7, Btot ≈ 60 μG, and Pe/k ≈ 5 × 10^5 cm^-3 K, with lower values in M33 and M31. Analysis of 18 Milky Way bones, assuming likely external pressures, also implies subcritical mass-to-flux ratios, consistent with polarization observations. These findings support consistency with pressure-bound, subcritical virial equilibrium rather than establishing it uniquely. The proposed explanation for low star formation efficiency is slow formation of filaments, clumps, and cores under strong magnetic fields, coupled with rapid dispersal by feedback and turbulence. Zeeman and DCF observations suggest that fields within clumps and cores can nevertheless permit collapse; MHD simulations predict star formation efficiencies of approximately 0.5–2%.

PublicSurveys show that larger molecular clouds gain mass with size more steeply than an early, widely used relation suggested. The authors fit these observations with a model in which magnetic fields and pressure from surrounding interstellar gas help clouds maintain a balance of forces. Fits involving about 1,500 clouds are consistent with this picture, and a separate analysis of 18 elongated Milky Way clouds gives similar indications, although it assumes likely surrounding pressures. This does not prove that all giant molecular clouds are in such a balance. If the interpretation is right, strong magnetic fields could slow the creation of smaller structures that form stars, while turbulence and stellar feedback disperse those structures rapidly. Observations suggest that magnetic fields inside dense clumps and cores can still allow collapse. Computer simulations predict low star formation efficiencies of about 0.5–2%; that range is a simulation prediction, not a new measurement from these cloud fits.

Young explorerStars can grow inside huge clouds of gas in space. Scientists compared many clouds with a math model and found that magnetic fields and a push from the gas around them might help keep the clouds balanced. That is a possible explanation, not something they have proved. The magnetic fields might make star-making pieces grow slowly, while stirring and pushes from stars break them apart. Some smaller pieces may still squeeze together to make stars. Computer models suggest that only a little of the cloud’s gas becomes stars.

ReveaLLAGN 3: Revealing the Infrared Spectral Energy Distributions of Low Luminosity AGN

David Ohlson, Anil C. Seth, Kameron Goold+18 more

AstronomerJWST observations trace the 1.7–24 μm spectral energy distributions of seven nearby low-luminosity AGN. Two-dimensional spatial fitting isolates unresolved nuclear spectra; comparison with aperture-based spectra demonstrates effective removal of host-galaxy contamination. Relative to more luminous AGN, the targets show enhanced near-infrared emission compared with X-rays, with the enhancement correlated with radio-loudness, but comparable mid-infrared-to-X-ray ratios. Most targets exhibit strong compact silicate emission, suggesting warm dust on parsec scales. Near-infrared slopes and colors are similar across AGN luminosities, whereas low-luminosity AGN typically have steeper mid-infrared slopes and redder colors. The strong silicate emission and steep mid-infrared slopes disagree with existing low-luminosity AGN spectral energy distribution models.

PublicUsing the James Webb Space Telescope, researchers studied infrared light from seven nearby galaxies with faint active centers. By separating the compact central light from surrounding galaxy light, they obtained cleaner views of these nuclei. Compared with brighter active nuclei, these faint centers emit more near-infrared light relative to their X-rays; this excess is linked to their relative radio strength. Their mid-infrared emission relative to X-rays is comparable to that of brighter nuclei. Most also show strong infrared signatures of silicate material, suggesting warm dust in a compact region around the center. Although their near-infrared light has similar spectral shapes to brighter nuclei, their mid-infrared light typically has steeper spectra and redder colors. These mid-infrared properties and strong silicate signatures do not agree with existing models for faint active galactic nuclei.

Young explorerScientists used the James Webb Space Telescope to look at seven nearby galaxies with dim, active centers. They separated light from each center from the light around it. Compared with brighter active centers, these dim centers give off extra amounts of one kind of invisible light when compared with their X-rays. Most also show a light pattern that suggests warm dust close to the center. Some of the patterns do not match what scientists’ current models say they should see.

Inside the cocoon: a comprehensive explanation of the spectra of Little Red Dots

A. Sneppen, D. Watson, J. H. Matthews+10 more

• High Energy Astrophysical Phenomena

AstronomerUsing grating spectra of 53 LRD-like objects, the authors find that self-consistent radiative-transfer models of supermassive black holes embedded in dense gas cocoons reproduce the spectra without requiring a stellar-like photosphere. Cocoons with comparable inflowing and outflowing mass fluxes reproduce the near-symmetric, electron-scattering-broadened emission lines. The same structure accounts for continuum shapes, hydrogen and helium equivalent widths, and absorption features. Predicted correlations among Balmer break strength, Balmer absorption, and scattering line width are confirmed in the sample. Metal-line absorption, X-ray weakness, and muted variability are additional model predictions. The inferred typical configuration contains a black hole of order one million solar masses within an ionised cocoon of tens of solar masses, likely supplied by a much larger cold-gas reservoir. The model offers an explanation for LRD spectra, although the population’s nature remains uncertain.

PublicJWST has revealed compact galaxies called little red dots whose nature is still uncertain. Researchers assembled spectra—the light separated into its different wavelengths—for 53 objects resembling these galaxies. Their calculations show that a supermassive black hole wrapped in dense gas can explain the detailed light patterns without needing a star-like outer surface. In the model, gas flows inward and outward at comparable rates, while scattering by electrons broadens emission features. The researchers also found predicted relationships between several spectral features in the observations. Other predictions, including weak X-ray emission and limited changes in brightness, are not presented here as confirmed findings. The model suggests typical black holes have about a million times the Sun’s mass, surrounded by ionised gas weighing tens of Suns and likely fed by a larger supply of cold gas.

Young explorerA space telescope has found tiny-looking red galaxies that puzzle scientists. Researchers studied the light from 53 objects like them. Their calculations suggest that a huge black hole wrapped in thick gas could make the light look this way. Some patterns they expected were also found in the real light. That is a clue that their idea could work, but scientists are still figuring out what these little red galaxies really are.

Axionlike dark-matter winds driven by galactic baryon redistribution

A.V. Nazarenko

AstronomerThis theoretical study models a spherical dwarf-galaxy dark matter halo as a Bose-Einstein condensate with axion-like interactions, examining its response to gravitational changes caused by baryonic redistribution. Linearized hydrodynamic simulations, parametrized using observations of NGC 2366, consider an expanding gas shell, a collapsing shell, and a stellar cluster contracting through dynamical friction in gas. Simulated central dark matter density changes remain within 0.01%, and induced dark matter flows reach only several meters per second, challenging prospects for detecting dark-wind signatures in this model. To address cumulative effects from repeated events, the authors develop a quantum excitation framework with a discrete spectrum under natural Robin boundary conditions. In the inhomogeneous halo, which contains an unstable phase region, the lowest long-wavelength radial mode acts as a false vacuum and undergoes non-viscous quantum relaxation with a calculated lifetime of 68 Myr. The framework yields universal exponential damping of the evolution operator; at the next perturbative order, nonlinear three-mode parametric exchange redistributes stable quasiparticle excitations rather than standard open-continuum Beliaev damping. These are model-dependent theoretical findings, not detections of condensate dark matter or its flows.

PublicCould moving ordinary matter stir dark matter inside a dwarf galaxy? This study explores that question under the unconfirmed assumption that dark matter forms a Bose-Einstein condensate, a collective quantum state, with axion-like interactions. Using observations of NGC 2366 to set up theoretical scenarios, the researchers simulated expanding and collapsing gas shells and an inward-moving star cluster. The simulated dark matter response was tiny: central density changes stayed within 0.01%, and flows reached only several meters per second, making such signatures difficult to detect. A separate quantum framework, developed to address the cumulative effects of repeated disturbances, predicts that one unstable collective mode decays over a characteristic 68 million years. The study describes possible behavior within this dark matter model; it does not establish that real dark matter has these properties.

Young explorerImagine a galaxy with invisible stuff called dark matter. Scientists used computer models to ask whether moving gas and stars could stir it. If dark matter behaves like the special quantum material they imagined, it barely moves in their tests. Their math also suggests that one kind of ripple slowly fades away. They have not seen dark matter doing this in a real galaxy.

Paschen Jumps in Little Red Dots: Evidence for Nebular Continua

Albert Sneppen, James H. Matthews, Darach Watson+6 more

AstronomerThe authors report evidence for Paschen continuum jumps in a high-signal-to-noise subset of high-redshift little red dots, consistent with hydrogen free-bound recombination to n=3. The sample’s Paschen and Brackett continuum shapes are consistent with minimally reddened nebular emission at electron temperatures of roughly 10,000 K or less. The Paschen signatures constrain scenarios in which the emission is thermalised. Recombination also naturally accounts for the extreme Hα equivalent widths and tight observed Hα–continuum correlation. These observations place upper limits on direct AGN accretion emission, stellar-atmosphere-like emission, and the fraction of line emission thermalised while traversing the cocoon, although the abstract gives no numerical limits. The authors interpret ionised-gas emission as a self-consistent explanation of the continuum, line strengths, and line profiles without multiple separately fitted components.

PublicLittle red dots are compact, reddish sources in the distant universe whose light has been difficult to explain. In a subset with particularly clear measurements, researchers report evidence for a distinctive change in the spectrum called a Paschen jump. This is consistent with light released when free electrons rejoin hydrogen atoms. The spectrum’s shape also fits gas at about 10,000 K or cooler, with little reddening by dust. This gas-based explanation naturally links the strong hydrogen emission lines to the broader background of light. The findings limit how much light could come directly from matter accreting onto an active galactic nucleus or from star-like atmospheres, but do not establish that those contributions are absent.

Young explorerAstronomers are studying tiny-looking red dots very far away. In some dots, they found clues that much of the light may come from gas, as tiny electrons join back onto hydrogen atoms. That could explain several things about the light at once, but scientists are still working out the whole story.

Clumps in a Cocoon: Geometry and Mixing Set the Universal X-ray to Hα Surface Brightness Ratio

Zirui Chen, S. Peng Oh, Drummond B. Fielding+3 more

AstronomerObservations show a nearly universal X-ray-to-Hα surface-brightness ratio of about 3 in galactic winds, ram-pressure-stripped tails, and cluster filaments, despite the different temperatures traced. Unlike plane-parallel mixing-layer models, these 3D wind-tunnel simulations at density contrast χ ≈ 10³ reproduce the ratio after smoothing on the tail-width scale. The simulated cold phase fragments into small Hα-emitting clumps within a volume-filling X-ray cocoon. The authors explain the correlation through a shared dependence on the hot-gas entrainment rate, which sets the bolometric luminosity. Hα carries a nearly fixed fraction determined mainly by atomic emissivity near 10⁴ K; the X-ray fraction depends on the residence-to-cooling-time ratio in the X-ray-emitting temperature band. An age diagnostic constrains residence times to be much shorter than cooling times, yielding comparable X-ray and Hα bolometric fractions. This simulation-based interpretation accounts for both the correlation and its order-unity ratio.

PublicObservations of galactic winds, gas tails stripped from galaxies, and filaments in galaxy clusters reveal a surprising pattern: their X-ray surface brightness is usually about three times their Hα surface brightness, even though these emissions trace very different gas temperatures. In three-dimensional computer simulations, cool gas breaks into small clumps surrounded by hot, X-ray-emitting gas. Averaging the simulated emission across the width of a tail reproduces the observed ratio. The researchers interpret this as a shared energy supply: both emissions scale with the rate at which hot gas is drawn into the mixture. Atomic emission physics regulates the Hα share, while the X-ray share depends on how long gas remains at X-ray-emitting temperatures compared with its cooling time. This offers a simulation-based explanation for the observed pattern.

Young explorerAstronomers see gas in space glowing in X-rays and in a special red light. The X-ray glow is usually about three times as bright. Computer experiments suggest that tiny cooler gas clumps sit inside hot gas. Both glows depend on hot gas joining the mix, which may explain why their brightnesses follow the same pattern.

MusE GAs FLOw and Wind (MEGAFLOW) XIV: Background-Galaxy Absorption Reveals Kiloparsec-Scale Structure in the Cool Circumgalactic Medium

Yucheng Guo, Nicolas F. Bouché, Martin Wendt+9 more

AstronomerThe study constrains the transverse coherence scale of cool, roughly 10^4 K circumgalactic gas by comparing mean and median stacked MgII equivalent-width profiles against extended background galaxies and effectively point-like quasars. The galaxy profiles are broadly consistent, whereas the quasar profiles differ significantly, reaching approximately 10 sigma beyond 100 kpc. Splitting galaxies by size yields broadly consistent mean and median profiles for sources with a median half-light radius of about 6.6 kpc, but an approximately 3-sigma difference for those around 1.5 kpc. These observations suggest an effective transverse coherence scale of a few kiloparsecs, broadly consistent with the roughly 2–7 kpc range probed by the galaxies, rather than a precise measurement of individual cloud sizes. A discrete-cloud toy model reproduces the qualitative differences through partial covering and beam averaging, supporting this geometric interpretation.

PublicResearchers studied the patchy, relatively cool gas surrounding galaxies by measuring how it absorbs light from more distant galaxies and quasars. Background galaxies provide broad patches of light, while quasars act almost like tiny points. Two ways of averaging the absorption measurements—the mean and median—gave broadly similar results for large background galaxies but different results for quasars and smaller galaxies. The pattern suggests that the absorbing gas stays coherent across distances of a few kiloparsecs. This is an estimate of its effective structure across our view, not a precise measurement of individual gas clouds. A simplified cloud model shows how incomplete coverage of the background light and averaging across a broad source can explain the observed pattern.

Young explorerSpace around galaxies has patches of gas that block a little light. Scientists looked through this gas at faraway galaxies and quasars. The galaxies look like wider lights, and the quasars look like tiny dots. The patterns in the blocked light suggest that the gas has patches stretching across very big distances. A simple pretend model of gas clouds helped explain the pattern, but the scientists still do not know the exact size of each cloud.

Morpho-kinematic of galaxies at cosmic noon

F. Rigamonti, F. R. Ditrani

AstronomerThe abstract motivates a proposed high-spatial-resolution stellar-kinematics program for massive galaxies at cosmic noon, around z~2. Local integral-field spectroscopy surveys find a weak correlation between morphology and dynamics and a continuum of bulge and disk kinematic properties, challenging the standard sequence of dispersion-supported bulge formation followed by secular disk growth. JWST imaging also reveals apparently mature morphological structures earlier than expected, but their dynamical nature requires confirmation with high-resolution stellar kinematics. The proposed observations would distinguish visually identified structures with different degrees of rotational support, probe central-region assembly, and investigate the co-evolution of mass, kinematics, and star formation. The abstract identifies VESPER-SHARP on the E-ELT as particularly suited to this program through its rest-frame optical coverage, spatial resolution, field of view, and multiplexing; it reports a proposal, not new kinematic measurements.

PublicA galaxy's appearance does not necessarily reveal how its stars move. Surveys of nearby galaxies find that structures called bulges and disks have overlapping patterns of stellar motion, complicating the traditional picture in which a bulge forms first and a disk grows later. JWST images also suggest that galaxies with seemingly mature structures existed earlier than expected, but images alone cannot confirm what those structures really are. The authors propose measuring stellar motions in massive galaxies around redshift 2, an era called cosmic noon, to investigate how their central regions formed and how galaxy mass, motion, and star formation developed together. They identify VESPER-SHARP on the E-ELT as well suited to these observations. These are proposed measurements, not completed results.

Young explorerA galaxy is a huge group of stars. Its shape in a picture does not always tell us how its stars are moving. Some pictures of the early universe show galaxies that look surprisingly grown-up, but scientists need to check how their stars move to understand them better. The researchers want to use a telescope tool called VESPER-SHARP to watch stars moving in faraway galaxies. This could help them learn how galaxies grow. They are describing a plan, not measurements they have already made.

A new era for Dual AGN science with SHARP

P. Severgnini, C. Vignali, A. De Rosa+21 more

AstronomerThe abstract presents the anticipated role of SHARP in obtaining a first statistical census and physical characterization of ultra-compact dual AGN, rather than reporting observational results. These systems contain two accreting massive black holes in one host galaxy, with projected separations from a few hundred parsecs down to a few parsecs. They are described as direct precursors of gravitationally bound, sub-parsec massive-black-hole binaries that emit strong low-frequency gravitational waves. SHARP is expected to bridge the observational gap between kiloparsec-scale pairs and these binaries, informing studies of black-hole growth, feedback, and galaxy–black-hole co-evolution across cosmic time. No measurements or demonstrated survey performance are supplied.

PublicTwo massive black holes can feed on surrounding material while sharing the same galaxy. The abstract focuses on especially close pairs, which may precede still tighter, gravitationally bound pairs that emit strong low-frequency gravitational waves. It presents SHARP as a future way to count and study these close pairs across cosmic distances, helping scientists understand how black holes and galaxies develop together. These are anticipated capabilities and scientific goals, not newly reported discoveries.

Young explorerA galaxy can have two giant black holes, both pulling in nearby stuff. Scientists want to find pairs that are very close together. They expect SHARP to help them find and study these pairs, giving clues about how black holes and galaxies grow. This describes what they hope to learn, not something they have already found.

A SHARP Look at Quenching and Bulge-Disk Growth in Massive Galaxies at Cosmic Noon

Chiara Mancini, Adriana Gargiulo, Alvio Renzini+11 more

• Instrumentation and Methods for Astrophysics

AstronomerThis prospective programme presents SHARP-VESPER IFS as a means to investigate the uncertain causal relationship between bulge assembly, star-formation quenching, and feedback. Combining ELT-class sensitivity, 31 mas spatial resolution, broad near-infrared coverage, and 12-IFU multiplexing, it would target massive galaxies with log(M*/M☉) ≥ 11 at 2.2 < z < 3.5, on the main sequence shortly before quenching or in the green valley. For typical 15-hour exposures, the authors predict continuum S/N > 15–20 per spectral resolution element in extracted inner-bulge and outer-disk spectra, and nebular-line S/N > 5 on sub-kpc scales. The proposed observations would separately constrain bulge and disk star-formation histories, ages, metallicities, and alpha enhancements, alongside spatially resolved star formation, gas kinematics, and feedback-driven outflows. Comparing the timing of bulge growth and star-formation suppression would test inside-out quenching and fast versus slow pathways; these are intended tests, not reported observational results.

PublicWhy massive galaxies stop making stars remains unclear. A growing central bulge is associated with this shutdown, but that does not establish what causes it. The authors outline a future observing programme using the SHARP-VESPER instrument to separate the light of central bulges and outer disks in distant, massive galaxies approaching or undergoing shutdown. They predict that typical 15-hour exposures would provide spectra detailed enough to reconstruct when each component formed its stars and to map glowing gas, its motion, and outflows. Comparing these histories could test whether star formation stops first in galaxy centres and whether shutdown happens quickly or slowly. The abstract describes expected capabilities and planned tests, not measurements establishing a cause.

Young explorerSome big galaxies stop making new stars, and astronomers do not yet know why. The authors describe a plan to use an instrument called SHARP-VESPER to study the middle and outer parts of faraway galaxies separately. They hope to learn when each part made its stars and how gas moves around. That could help them find out whether a galaxy stops making stars in its middle first, and whether it stops quickly or slowly. These are planned observations, not answers they have already found.

Probing IMF Variations in High-Redshift Early-Type Galaxies with SHARP

F. La Barbera, G. De Lucia, F. Ditrani+9 more

AstronomerThe abstract motivates high-redshift tests of a time-dependent stellar initial mass function (IMF). Local early-type galaxies show evidence from spectroscopy, dynamics, and lensing for bottom-heavy central IMFs, with radial gradients toward Milky Way-like distributions. In contrast, the chemical enrichment of massive early-type galaxies implies an important contribution from massive stars during early formation. An initially top-heavy IMF followed by a low-mass-dominated IMF could reconcile these findings, but this evolutionary scenario and its physical origin lack direct observational confirmation. Direct IMF measurements at z>1, including constraints on dwarf-to-giant and stellar mass-to-light ratios, are needed. The authors forecast that SHARP on the E-ELT will enable spatially resolved spectroscopy of IMF-sensitive features in early-type galaxies out to z~3; this is a prospective capability, not a reported high-redshift measurement.

PublicStars are born with a range of masses, and that mix helps shape how galaxies evolve. Observations of nearby early-type galaxies indicate an unusually large proportion of low-mass stars in their dense centers, with a more Milky Way-like mix farther out. Yet their chemical enrichment suggests that massive stars played a major role early on. One possible explanation is that these galaxies formed relatively more massive stars first and more low-mass stars later. That change over time has not been directly confirmed. The authors expect the SHARP instrument on the E-ELT to help test this idea by examining light from different parts of distant galaxies.

Young explorerGalaxies make stars of different sizes. Astronomers see signs of many small stars in the centers of some nearby galaxies, but other clues suggest big stars were important long ago. Maybe the mix changed as the galaxies grew older. That is not yet proven. A future tool called SHARP could help check.

Probing the dynamics of extreme galaxies I. Dark matter content in ultra-diffuse galaxies

Filippo Bouchè, Chiara Buttitta, Saboura Zamani+6 more

• Cosmology and Nongalactic Astrophysics

AstronomerIntegral-field stellar kinematics of the LEWIS ultra-diffuse galaxy UDG-1 and extended dwarf LSB-6 reveal coherent rotation with a non-negligible random-motion component and no signs of ongoing disturbance. The authors model dwarf-thickness stellar spheroids embedded in spherical dark matter halos, comparing two-dimensional velocity fields with observations in a Bayesian framework. The data favor a cuspy halo for UDG-1 and a cuspless halo for LSB-6, but cannot conclusively distinguish cold, fuzzy, self-interacting, and non-minimally coupled dark matter; all tested alternatives remain viable. Conditional on fuzzy dark matter, inferred boson masses are mutually consistent: 4.7 (+1.8/-1.1) × 10^-22 eV for UDG-1 and 6.3 (+0.4/-0.4) × 10^-22 eV for LSB-6. For self-interacting dark matter, LSB-6 provides a reported robust constraint of ⟨σv⟩/m = 14.3 (+2.0/-1.9) cm² km g^-1 s^-1. Upper limits on the non-minimal coupling length imply only marginal deviations from ΛCDM, rather than a detection of such deviations. Across the tested models, both galaxies have dark matter contents comparable to typical dwarf halos at similar stellar masses. Combined with stellar-population and globular-cluster information, the findings support, but do not establish, a puffed-up dwarf origin.

PublicResearchers studied how stars move inside two faint, spread-out galaxies, UDG-1 and LSB-6. Both rotate in an orderly way, although their stars also have substantial random motions, and neither shows signs of being disturbed now. By comparing the observations with models of the stars and surrounding dark matter, the team found that UDG-1 favors dark matter concentrated toward its center, while LSB-6 favors a distribution without a sharp central peak. These inferences depend on the modeling assumptions. Several different dark matter theories can explain the data, so the study does not establish which is correct. In every tested model, the galaxies contain amounts of dark matter comparable to ordinary dwarf galaxies with similar stellar masses. Together with evidence from their stars and star clusters, this supports the idea that they began as dwarf galaxies that became more spread out, rather than proving that history.

Young explorerScientists watched how stars move in two very faint galaxies. The stars turn around together, but they also move in different directions. Scientists compared those movements with ideas about invisible matter called dark matter. More than one idea could fit, so they still do not know which is right. The clues suggest these galaxies may be small galaxies that spread out and became puffier, but that is not certain.

Stellar bar occurrence in TNG50 and TNG100: disentangling environmental effects and assembly history at z = 0

Karol Chim-Ramirez, Bernardo Cervantes-Sodi, Yetli Rosas-Guevara

AstronomerUsing TNG50 and TNG100 at z=0, the study examines bars in satellite disc galaxies within 2 R200, with stellar-mass thresholds of 10^9 and 10^10 solar masses, respectively. The samples contain 859 TNG50 and 1719 TNG100 satellites. The simulations recover the morphology-density relation: thin-disc fractions increase with cluster-centric distance and decrease with host halo mass. Bar fractions and bar radii normalized by effective radius decline mildly with cluster-centric distance, while absolute bar radii remain constant. At fixed distance, bar fractions increase with halo mass, partly reflecting the presence of more massive galaxies in more massive haloes. Earlier-assembled galaxies have higher bar fractions, especially within 0.5 R200, suggesting an association rather than establishing causation. Overall, the simulated environmental dependence is mild, with stronger connections to stellar mass and assembly history.

PublicThis study uses two computer simulations, rather than telescope observations, to investigate how a galaxy’s surroundings relate to whether it has a central bar. Among the simulated satellite disc galaxies, bars are slightly more common closer to the host system’s centre and in more massive host haloes. The latter trend is partly explained by more massive galaxies living in more massive haloes. Bar lengths stay constant in absolute terms, although their size relative to the galaxy’s effective radius decreases slightly farther from the centre. Galaxies that assembled earlier are also more likely to have bars, particularly near the host system’s centre. The results suggest that environment has a modest connection to bars, while a galaxy’s stellar mass and assembly history are more strongly linked to their presence; they do not establish what causes these relationships.

Young explorerSome galaxies have a bar-shaped middle. Scientists studied pretend galaxies inside computers to see where these bars appear. In their computer worlds, galaxies nearer the middle of a big group were a little more likely to have bars. Galaxies that came together earlier were also more likely to have them. Where a galaxy lives seemed to matter a little, but how much star material it has and when it came together were more closely linked to having a bar. These are clues from computer models, not proof of what makes a bar.

An ALMA sub-kiloparsec test of the Kennicutt--Schmidt relation in a strongly lensed dusty star-forming galaxy at z∼2.78

C. Cornil-Baïotto, J. Molina, G. Mahler+9 more

AstronomerALMA observations of SMMJ0658, a main-sequence star-forming galaxy at z=2.7768 ± 0.0002 magnified approximately 20-fold by the Bullet Cluster, probe the resolved Kennicutt–Schmidt relation near cosmic noon. A JWST-based lens model reconstructs CO(3–2) and rest-frame 803 μm continuum emission at approximately 200 pc resolution. The inferred clump properties include molecular gas surface densities of approximately 1.3–2.3 × 10³ solar masses pc⁻², star formation rate surface densities of 0.5–2.3 solar masses yr⁻¹ kpc⁻², and depletion times of 0.82–2.56 Gyr. Spatial decorrelation between CO and dust produces strongly scale-dependent depletion times. The authors find a KS-relation breakdown scale of 0.8 ± 0.1 kpc, consistent with individual regions sampling different stages of the star-formation cycle. This extends a pattern previously observed locally and to z≈1 to a galaxy at z≈2.78. ALMA and JWST also provide evidence for a lensed galaxy pair, but an early-stage interaction involving SMMJ0658 remains uncertain.

PublicAstronomers used ALMA to examine gas and dust in a distant galaxy from near the peak era of cosmic star formation. The Bullet Cluster acts as a gravitational lens, magnifying the galaxy about 20 times; a lens model based on JWST data lets the team reconstruct details roughly 200 parsecs across. They find dense star-forming clumps and show that the usual relationship between gas supply and star formation breaks down below about 800 parsecs in this galaxy. Gas and dust emission do not line up precisely, making inferred gas-consumption times depend strongly on the area measured. The authors interpret this as consistent with different regions being at different stages of forming stars. There is also evidence for a galaxy pair, but whether the galaxies are beginning to interact is uncertain.

Young explorerA big group of galaxies acts like a magnifying glass, helping astronomers study a very faraway galaxy. They found thick clumps of gas where stars are forming. When they looked at small patches, the usual rule linking gas to star-making did not work well. The patches might be at different steps in making stars. The galaxy may also have a nearby partner, but scientists are not sure whether the two are starting to interact.

Beyond the Disc--Spheroid Dichotomy at 0.6 < z < 8.0: Evidence for a Morphological Indeterminacy Regime from JWST

Igor Kolesnikov, Reinaldo Ramos de Carvalho, Jeong Hwan Lee+3 more

AstronomerThe study compares galaxy morphology classifications over 0.6 < z < 8.0 using JWST observations of 15,567 galaxies and 6,099 synthetic galaxies from IllustrisTNG. Its unsupervised-supervised hybrid machine-learning approach uses the non-parametric MEGG system, combining the second moment of the light distribution, entropy, Gini, and Gradient Pattern Analysis without relying on visual labels or prescribed light profiles. Parametric and non-parametric classifications broadly agree at z < 2.5 but systematically diverge at higher redshift. The authors call this the Morphological Indeterminacy Regime (MIR), where classical disc and spheroidal categories do not uniquely describe the population; the mixed-interpretation fraction reaches approximately 0.55 at z > 2.5. Cross-domain and projection-invariance tests support classification stability across data sets and viewing angles. At 2.5 < z < 8.0, MIR galaxies have a median log(M_star/M_sun) of approximately 9.7, between discs at 9.5 and spheroids at 10.1; irregular galaxies have mass distributions similar to MIR galaxies. The interpretation that MIR systems are dynamically young galaxies not yet settled into the classical Hubble sequence is an inference from these findings, rather than a direct dynamical measurement.

PublicMany early galaxies may not fit neatly into familiar shape categories. This study compares ways of classifying galaxies using JWST observations of 15,567 galaxies alongside 6,099 simulated galaxies. A machine-learning method measures patterns in their light without depending on human-assigned shape labels or preset light profiles. Classification methods broadly agree below a redshift of 2.5, but disagree systematically at higher redshifts, which correspond to earlier cosmic times. In that earlier period, about 55% of galaxies receive mixed interpretations rather than a unique disc or spheroidal classification. Tests suggest that these classifications are stable across data sets and viewing angles. Galaxies with mixed interpretations typically have stellar masses between those of discs and spheroids, and mass distributions similar to irregular galaxies. The researchers interpret the ambiguity as a sign that many early galaxies were still assembling and had not yet settled into familiar shapes; the study does not directly establish their dynamical state.

Young explorerGalaxies are huge groups of stars, and scientists sort them by how they look. The researchers studied telescope pictures and pretend galaxies made in a computer. For galaxies seen when the universe was younger, different sorting methods often gave different answers about their shapes. More than half of the galaxies in that early group were hard to put into just one shape box. The researchers think these galaxies may still have been growing and settling into shape, but that is an explanation of what they found, not something they watched happen.

Unveiling the nonthermal environments of NGC 3411 and NGC 5903 through new MeerKAT observations

T. Pasini, F. De Gasperin, E. O'Sullivan+5 more

• Cosmology and Nongalactic Astrophysics

AstronomerNew MeerKAT UHF- and L-band observations characterize diffuse nonthermal emission in two selected galaxy groups, NGC 3411 and NGC 5903, with context from previously analyzed archival Chandra and XMM-Newton data. In NGC 3411, emission extends approximately 70 kpc around the central AGN and contains newly resolved arcs on scales of approximately 20–30 kpc. Its spectrum is relatively uniform and steep, with α approximately −1.7. The origin remains unresolved: the authors discuss mini-halos, aged AGN plasma, weak shocks, and a radio galaxy viewed along the line of sight. NGC 5903 shows complex radio filaments and a previously unknown ring-like structure around its central AGN. The northern arc exhibits localized spectral flattening to α approximately −0.9; polarization reveals ordered magnetic fields and a patchy rotation measure distribution. Together with disturbed X-ray morphology, these observations support, but do not establish, redistribution and local reenergization of fossil AGN plasma by group-scale turbulence, shear, and weak compression. The study highlights the diagnostic value of sensitive, high-resolution, multifrequency radio observations.

PublicNew MeerKAT radio observations reveal intricate structures around the active centers of two galaxy groups. In NGC 3411, the researchers detect extended radio emission spanning about 70 kiloparsecs, including previously unseen arcs. Its origin is uncertain: possibilities include old material from the active galactic nucleus, weak shocks, a diffuse radio mini-halo, or a radio galaxy viewed along our line of sight. In NGC 5903, the observations reveal filaments and a newly identified ring-like feature. Radio measurements also show local changes in the emission spectrum and organized magnetic fields. Combined with earlier X-ray evidence of disturbed gas, these findings support an interpretation in which motions within the group have moved old material from the active nucleus and given it fresh energy in some places. That explanation is supported by the evidence rather than definitively proven.

Young explorerAstronomers used a radio telescope to look at two families of galaxies. They found faint arcs around the middle of one family, and threads and a ring in the other. They are not sure what made the first family's arcs. In the second, they think moving gas may have stirred up old material from the galaxy's active center and given it more energy, but they have not proved that yet.

Characterizing Gravitational Wave Electromagnetic Counterparts with the Schmidt Observatory System

Keerthi Kunnumkai, Antonella Palmese, Thomas Wevers+7 more

AstronomerMotivated by the observed GW170817–kilonova association, this study simulates kilonova detection prospects at the sensitivity expected for the fifth LIGO/Virgo/KAGRA observing run (O5). Predicted binary neutron star kilonova detection rates are 0.3–4.2 per year for Argus and 0.6–7.0 per year for Rubin; Rubin could also detect up to one neutron star–black hole kilonova per year. Lazuli is projected to characterize the population down to approximately g = 26 mag as early as 12 hours after merger, while roughly 35% of events are expected to have jet afterglows detectable by DSA. These are forecasts, not observed yields. The study also characterizes kilonova spectra to identify observable signatures of heavy-element production and develops a strategy combining high-cadence imaging with spectral monitoring to constrain ejecta properties and composition within reasonable Lazuli observing time.

PublicThe detection of gravitational waves from GW170817 and its accompanying kilonova showed how studying both space-time ripples and light can reveal details of compact-object mergers. But kilonovae are faint and change quickly, making it difficult to build a large sample. This study uses simulations to forecast what improved gravitational-wave detectors and planned telescope observations could achieve. For mergers of two neutron stars, Argus could find 0.3–4.2 kilonovae per year and Rubin 0.6–7.0. Rubin could also find up to one per year from a neutron star merging with a black hole. The authors predict that Lazuli could study faint kilonovae as early as 12 hours after merger and that DSA could detect jet afterglows from about 35% of events. They also develop an observing plan to investigate the expelled material and signs of heavy-element production. These prospects are predictions, not new detections.

Young explorerWhen two neutron stars crash together, they can make ripples in space and a faint glow that changes quickly. Scientists have already seen one such glow along with the ripples. In this study, they used computer simulations to work out how telescopes might find and study more of these glows. They also made a plan to look for clues about the heavy elements made in the crashes. These are predictions and plans, not new glows they have found.

One gravitational function across matter phases: compatibility and interface constraints in static f(R,T) gravity

Samuel Isidoro dos Santos Júnior, Rafael C. R. de Lima

AstronomerThis theoretical study tests whether a single conservative f(R,T)=R+h(T) model can accommodate two matter phases across a sharp Maxwell interface. The analysis is static and local, assuming spherical symmetry, the L_m=rho closure, cold barotropic perfect fluids, and no surface layer. A common h must satisfy both phase-specific reconstruction equations wherever their occupied trace ranges overlap, and must ensure continuity of effective normal pressure; matching material pressure and chemical potential alone is insufficient. For a hadronic polytrope with K>0 and Gamma>1 and an affine quark equation of state, an open overlap forces h to be constant on both occupied ranges. For separated ranges, the authors explicitly construct a nonconstant C² function satisfying both requirements at one interface. This local construction has additional limits: extending the same polytrope to zero density and requiring regularity at T=0 removes its nonconstant part there, while separate conservation forbids density changes of a fluid element wherever h'(T) is nonzero.

PublicCan one modification of gravity consistently describe two forms of matter meeting at a sharp boundary? This mathematical study examines that question under restricted, static conditions, rather than through observations. Each form of matter constrains the same gravity-modifying function, and the boundary imposes an extra requirement: the effective pressure normal to it must match on both sides. Equal ordinary pressure and chemical potential do not guarantee this. For the two matter models studied, overlapping ranges of the quantity that controls the modification force the function to be constant across both ranges. If those ranges are separated, the authors construct a smooth, nonconstant function that works locally at one boundary—not a complete global solution. Further restrictions arise when the matter model extends to zero density, and conservation prevents a fluid element's density from changing wherever the modifying function has a nonzero slope.

Young explorerImagine two kinds of stuff touching, with one gravity rule that must work for both. The researchers used math to see whether that is possible. For the kinds they studied, if both need the rule for some of the same numbers, the rule must stay constant. If they need it for separate sets of numbers, the researchers can make a changing rule work where the two kinds meet. But this only shows that it works near one meeting place, not everywhere.

A high-frequency turnover in the persistent radio source of FRB20201124A

G. Bruni, G. Gianfagna, L. Piro+8 more

• Solar and Stellar Astrophysics

AstronomerArchival ALMA Band 3 observations near 100 GHz were combined with existing VLA measurements at 6, 15 and 22 GHz to constrain the centimetre-to-millimetre spectrum of the persistent radio source associated with FRB20201124A. A two-parameter Granot–Sari broken-power-law fit in the slow-cooling regime, using Bayesian nested sampling, gives a peak frequency of 63 GHz with uncertainties of −33/+100 GHz and a peak flux density of 28 ± 9 μJy. The spectrum remains flat or inverted through 22 GHz, and the inferred peak frequency is the highest among known persistent radio sources associated with repeating FRBs. The fit is consistent with young, rotation-powered magnetar wind-nebula models, which predict a peak in this range and self-absorption below approximately 0.5 GHz. The authors interpret the source as a strong candidate for the youngest magnetar associated with a repeating FRB, with an age of approximately 20 years or less; neither the magnetar interpretation nor this age is established directly by the observations.

PublicThe repeating fast radio burst FRB20201124A has an associated steady radio source whose brightness stays level or rises toward unusually high radio frequencies. Researchers combined existing radio measurements with archival observations near 100 GHz. Their model fit places the spectrum’s brightness peak near 63 GHz, although the uncertainty is large. This is the highest inferred peak frequency among known steady radio sources associated with repeating fast radio bursts. The findings fit expectations for a cloud powered by the rotation of a young magnetar, a highly magnetic neutron star. The authors suggest it could be the youngest magnetar linked to a repeating fast radio burst, perhaps about 20 years old or younger, but this explanation and age remain interpretations rather than confirmed measurements.

Young explorerAstronomers studied a steady radio glow near something that sends out repeated, quick radio flashes. They checked how bright the glow is at different radio frequencies. Its pattern could come from a cloud powered by a very young, strongly magnetic star. That idea fits the clues, but they have not proved it yet.

Insights on the mass composition of ultrahigh-energy cosmic rays from small-scale anisotropy with large-scale structure simulations

Ryo Higuchi, Eiji Kido, Shigehiro Nagataki

AstronomerUsing Pierre Auger Observatory open data, the authors confirm no significant small-scale arrival-direction anisotropy above 100 EeV within 3 degrees. They interpret this near-isotropy as potentially arising from heavy nuclei propagating farther before photodisintegration, sampling a more nearly homogeneous galaxy distribution. Mock observations use the Millennium Run semi-analytic galaxy catalog, pure-proton, pure-iron, or pure-uranium compositions, and varying source densities and turbulent extragalactic magnetic fields. Within these models, the observed isotropy excludes the pure-proton and pure-iron cases without magnetic fields. Pure uranium can reproduce it for high source density and a turbulent field; strong turbulence permits both iron and uranium, while almost no tested proton parameter set matches the observation. These are model-dependent constraints on composition, source density, and field strength, not a detection of uranium cosmic rays.

PublicThe researchers examined public Pierre Auger Observatory data for cosmic rays above 100 EeV and found no statistically significant clustering of arrival directions within 3 degrees. They suggest that heavy atomic nuclei could help explain this nearly uniform pattern: such particles may travel farther before breaking apart, allowing them to arrive from a more evenly distributed population of galaxies. To test this interpretation, they simulated skies made entirely of protons, iron nuclei, or uranium nuclei while changing how common the sources were and how strong the turbulent magnetic fields were. Without magnetic fields, the proton and iron models were incompatible with the observed uniformity. With strong turbulent fields, both iron and uranium models could fit, whereas almost none of the tested proton models could. The study narrows possible explanations but does not establish what the particles are made of.

Young explorerScientists looked at where some very energetic space particles seem to come from. They did not find clear little bunches in the sky. They made pretend skies on computers to see why. Some pretend skies with heavy particles and tangled magnetic fields looked like the real pattern. Almost none made only with protons, a lighter kind of particle, did. That gives scientists clues, but it does not tell them for sure what the real particles are.

Unsupervised Neural Operators for Rotating Relativistic Stars: High-Fidelity Equation of State Inference and Pulsar Spin Evolution at Scale

Anarya Ray

• Artificial Intelligence
• Machine Learning
• General Relativity and Quantum Cosmology

AstronomerThe authors develop physics-informed neural operators for the axisymmetric general-relativistic hydrostatic-equilibrium equations governing rotating neutron-star interiors. Training is fully unsupervised, with an objective based solely on the governing partial differential equations. They report a 1,000-fold computational speed-up with negligible accuracy loss. The motivation is to avoid biases from non-rotating models or approximate rotational corrections when inferring the dense-matter equation of state and modeling neutron-star populations. The solvers make repeated, rotation-consistent structure calculations computationally accessible for equation-of-state inference and binary-evolution population synthesis, including propagation of equation-of-state uncertainties into spin predictions. These are computational capabilities, not new observational constraints or reported population predictions.

PublicRapidly spinning neutron stars can help scientists investigate extremely dense matter, but calculating their internal structure is computationally expensive. The authors report a neural-network-based solver that learns from the equations of physics alone, rather than from example solutions. It solves the equations for rotating neutron stars about 1,000 times faster, with negligible loss of accuracy. This could make it practical to include rotation more consistently when interpreting measurements and modeling how neutron-star populations evolve. The reported advance is a calculation method, not a new measurement of what neutron stars contain.

Young explorerSome stars spin very, very fast, and working out what happens inside them takes computers a long time. Scientists made a new computer helper that learns from physics rules. They say it can do these calculations about a thousand times faster while keeping almost the same accuracy. It could help scientists study these stars, but it has not yet told them what is inside.

A Laplace-Transform Green's Function for Two-Zone Diffusion with Energy Losses: Application to the Geminga Pulsar Halo

Furong Li, Wei Liu, Yali Shao+1 more

AstronomerExtended TeV gamma-ray halos around pulsars are commonly interpreted as indicating electron and positron diffusion roughly two orders of magnitude slower than the Galactic average inferred from B/C measurements. This work derives an analytical Green's function, using a Laplace transform, for spherically symmetric two-zone diffusion with a discontinuous diffusion coefficient at r_b. The solution preserves particle-density and diffusive-flux continuity and recovers the Gaussian kernel in the one-zone limit. For the comparison parameter set, both the spatial kernel and the predicted positron flux at Earth agree numerically with an independent integral solution. Applied to Geminga, the examined two-zone models yield a more extended outer particle distribution, broader positron spectra, and higher TeV positron fluxes than the homogeneous model. The assumed injection model also changes the high-energy peak's height and shape. The predicted gamma-ray surface-brightness profile reproduces the main radial decline observed by HAWC, rather than establishing a unique diffusion or injection model.

PublicLarge halos of very-high-energy gamma rays around pulsars are often interpreted as evidence that energetic electrons and positrons spread unusually slowly near these sources. The researchers develop an exact mathematical solution for a simplified model with two regions: slow particle spreading near the pulsar and faster spreading farther away. Their solution matches an independent calculation for the set of parameters tested. When applied to the pulsar Geminga, the models predict particles reaching farther into the surrounding region and a broader range of positron energies, with more positrons reaching Earth at TeV energies than in the uniform-diffusion model used for comparison. These predictions also depend on how particles are assumed to be supplied by the pulsar. The predicted fading of the gamma-ray halo with distance from its center reproduces the main trend observed by HAWC, but this agreement does not establish the model as the only explanation.

Young explorerSome spinning stars called pulsars have big halos of very energetic light. Scientists think tiny particles may move around slowly near a pulsar, then spread faster farther away. The researchers made a math model of this idea and tried it for a pulsar called Geminga. The model predicts that particles spread farther out than in a model where they spread the same way everywhere. It also makes a halo that fades outward much like the one scientists see. That is a useful match, but it does not prove the idea is the only right one.

The kinematic Kelvin-Helmholtz instability-driven dynamo: implications for merging compact objects

James R. Beattie, Amitava Bhattacharjee, Elias R. Most+4 more

• Astrophysics of Galaxies
• Solar and Stellar Astrophysics
• Fluid Dynamics

AstronomerUsing an ensemble of high-resolution visco-resistive simulations of Kelvin–Helmholtz-instability-driven dynamos, the authors construct analytical models for magnetic growth rates and mean vertical field onset times in the high-Reynolds-number limit. The models suggest immediate seeding of the mean vertical field, kinematic growth rates that become independent of Reynolds number asymptotically, and departure from the kinematic stage on roughly 0.1 ms timescales, with magnetar-strength fields attained during that transition. These simulation-based extrapolations suggest that most global binary neutron star merger simulations do not temporally resolve the relevant dynamo regime; they are not observational measurements of merger magnetic fields.

PublicWhen two neutron stars merge, the sliding motion between them can become unstable and drive a process that amplifies magnetic fields. The researchers used many high-resolution computer simulations of this process to build mathematical models of how quickly the fields develop. In the limit of very large Reynolds number, their models suggest that a vertical magnetic field begins forming immediately and can reach magnetar strength as the initial growth stage ends, on a timescale of about a tenth of a millisecond. This is a model-based prediction, not an observation, and suggests that most whole-merger simulations use time steps too coarse to capture this magnetic growth correctly.

Young explorerWhen two very dense stars crash together, swirling material can make their magnetism stronger. Scientists used computer experiments to study how this might happen. Their models suggest the magnetism could become extremely strong very quickly—so quickly that other computer models might miss it. They have not watched this happen in real stars.

Longitudinal-field particle acceleration in channels generated by strong electromagnetic waves in pair plasma

Kavin Tangtartharakul, Andrei M. Beloborodov, Carolina Herrera Hernandez+2 more

AstronomerA three-dimensional kinetic particle-in-cell simulation examines a relativistically strong electromagnetic wave of finite transverse width incident on a cold, uniform pair plasma. In the simulation, the wave advances by creating a fully evacuated channel rather than penetrating the plasma. Its energy loss exceeds that required for plasma clearing alone. The study attributes the excess loss to strong particle acceleration near the channel walls, driven by a longitudinal electric field associated with the wave’s transverse structure and the self-generated channel geometry. These are simulation findings; future high-power-laser experiments are mentioned as a possible setting, not as an experimental demonstration.

PublicA computer simulation explores how an extremely intense electromagnetic wave interacts with a plasma made of particles and their antiparticles. Rather than passing through the plasma, the wave pushes it aside and advances by carving out an empty channel. The simulated wave loses more energy than clearing that channel alone can explain. The researchers find that the extra energy goes into accelerating particles near the channel walls, through an electric field linked to the wave’s shape and the channel it creates. Such interactions may become accessible in future high-power-laser experiments, but this study reports a simulation, not a laboratory observation.

Young explorerScientists used a computer to see what a very strong wave would do when it met a cloud of tiny particles and their opposite partners. In the computer, the wave pushed the particles aside and made an empty tunnel. It also gave some particles near the tunnel walls a big boost, using more of its energy than just making the tunnel would take. This happened in a computer simulation, not in a real experiment.

Optical linear polarization of the Be--X-ray pulsar binary LS V +44 17

Anagha P. Nitindala, Andrei V. Berdyugin, Alexandra Veledina+8 more

• Solar and Stellar Astrophysics

AstronomerOptical BVR polarimetry of the Be–X-ray pulsar binary LS V +44 17 during its early-2023 giant outburst and over the subsequent three years reveals significant, time-variable polarization of approximately 1.1–2.1%, including the interstellar contribution. The inferred interstellar polarization is approximately 2.5–2.9%; correcting for it yields intrinsic polarization of 0.5–1.7%, oriented perpendicular to the interstellar polarization direction. From the temporal and spectral evolution, the authors infer that scattering in the Be decretion disk is the dominant source of intrinsic optical polarization. The changing intrinsic polarization position angle hints at possible disk precession but does not establish it.

PublicAstronomers measured the alignment of light waves, called polarization, from the binary system LS V +44 17 during a giant outburst in early 2023 and over the following three years. The measured polarization changed significantly with time. After correcting for polarization contributed by material between the system and Earth, they estimate that the system itself produces polarization of 0.5–1.7%, oriented perpendicular to the interstellar contribution. The way the polarization changes with time and across optical colors suggests that light scattering in the disk around the Be star is its main source. Changes in the alignment direction may indicate that the disk slowly changes its orientation, or precesses, but this remains an interpretation rather than a confirmed finding.

Young explorerScientists watched light from a pair of stars during a big bright burst and for three years afterward. They found that the light waves lined up in a way that changed over time. Some of that lining up happened as the light traveled to us, so they worked out what was left from the stars themselves. They think light bouncing around in a disk of material around one star causes most of it. The disk might also be slowly wobbling, but they are not sure.

A search for sterile neutrinos at ultrahigh energies at the Pierre Auger Observatory

Pierre Auger Collaboration, A. Abdul Halim, P. Abreu+97 more

• High Energy Physics - Phenomenology

AstronomerThe study evaluates Pierre Auger Observatory sensitivity to MeV–100 MeV sterile neutrinos in a minimal 3+1 model, with one sterile state mixing predominantly with tau neutrinos. At ultrahigh energies, the resulting mass eigenstate N1 could traverse substantial Earth chords and interact through its active component, producing tau leptons that emerge and decay into atmospheric air showers. Detailed Monte Carlo calculations include neutrino propagation and interactions, tau energy losses, and decay. From the calculated exposures, the authors derive a 90% confidence upper limit on an isotropic diffuse N1 flux: E^2 Phi_N ≤ 2 × 10^-9 sin^-2(theta_N) GeV cm^-2 sr^-1 s^-1 over 0.3–200 EeV, assuming an E^-2 spectrum and sin^2(theta_N) ≲ 0.1. They also derive mixing-angle and dark-matter-lifetime constraints for N1 production by superheavy dark-matter decay, using a benchmark dark-matter mass of 10^13 GeV and sterile-neutrino masses of 10 and 100 MeV. These are model-dependent constraints and sensitivity calculations, not a reported sterile-neutrino detection.

PublicCould the Pierre Auger Observatory help search for hypothetical particles called sterile neutrinos? This study calculates how ultrahigh-energy sterile neutrinos might travel through Earth and, through a small connection to ordinary tau neutrinos, produce tau particles near the surface. Those tau particles could escape and decay in the atmosphere, creating showers of particles the observatory could detect. Using detailed computer simulations, the researchers derive upper limits on how many sterile neutrinos could arrive from all directions, under specific assumptions about their energies and mixing with ordinary neutrinos. They also constrain scenarios in which these particles come from the decay of extremely massive dark matter. The work explores the observatory’s reach; it does not report finding sterile neutrinos or dark matter.

Young explorerScientists used computers to study whether tiny, hard-to-catch particles might pass through Earth and help make a shower of other particles in the air. A big science observatory could look for those showers. The study helps show what it could search for, but it does not say these hidden particles were found.

The Environment of High-Energy Transient Host Galaxies at High Redshifts as Observed by SHARP

L. Izzo

• Astrophysics of Galaxies

AstronomerThis review motivates spatially resolved near-infrared IFU observations of high-redshift transient hosts rather than reporting new measurements. Galaxy-integrated properties can misrepresent progenitor environments because of metallicity gradients and spatial inhomogeneity. The authors highlight high-spatial-resolution data from instruments such as SHARP/VESPER as a means to determine explosion-site metallicity, stellar age, and kinematics. The scientific goals include connecting long-GRB progenitors and their low-metallicity requirement to birth environments, and characterizing hosts of SNe without associated GRBs and of kilonovae.

PublicA galaxy-wide average can hide the conditions in the particular neighborhood where a cosmic explosion occurred. This review argues for using detailed near-infrared observations to map those neighborhoods, including their chemical makeup, stellar ages, and motions. Instruments such as SHARP could help connect gamma-ray bursts and other brief cosmic events in the early Universe to their surroundings. The abstract describes the case for these observations and their potential, not new measurements of explosion sites.

Young explorerA galaxy is a huge home for stars, and its neighborhoods can be different. To learn about a big flash in space, scientists want to look closely at where it happened, not just at the whole galaxy. This paper explains how special tools could help them do that. It does not report new discoveries about a particular flash.

APOLLO-Timing: Annealed Phase - Orbit Lattice Linking across Observations for Binary Pulsar Timing

Y. R. Wen, D. Zhao, N. Wang+5 more

• Solar and Stellar Astrophysics

AstronomerAPOLLO-Timing jointly fits timing parameters and integer inter-session pulse offsets using a Bayesian phase-orbit lattice, with PINT checking candidate connections at fixed pulse numbers. Applied to PSR J1912-1215, it finds a unique best-supported phase connection for 96 TOAs across 23 sessions spanning 1438.07 days, where a preliminary Keplerian fit had failed to phase-connect the data. The search uses the preliminary position, F0 and F1 estimates and fixes the dispersion measure, but requires no supplied orbital parameters. A repeat full-data blind search recovers the same pulse counts in 914.0 s, including the final fit; searches of 17-, 18- and 19-session subsets also recover the reference path with initial F1 set to zero. The solution yields Pb = 17.526 days, x = 23.448 light-seconds, e = 2.65e-5, chi-square = 188.01 and weighted rms residual = 5.08 microseconds. Assuming a 1.4-solar-mass pulsar and 60-degree inclination gives a companion mass of 0.67 solar masses, favoring a CO/ONeMg white dwarf.

PublicLong gaps between observations can make it difficult to count a pulsar’s pulses correctly and determine its orbit. Researchers developed APOLLO-Timing to solve both problems together, then applied it to observations of PSR J1912-1215. Using 96 pulse arrival measurements from 23 observing sessions, the method found one best-supported way to link the pulses across the gaps, where an earlier fit had failed. It recovered an almost circular, 17.526-day orbit without being given orbital parameters, although it used other starting estimates and held the radio-wave dispersion measure fixed. Repeat searches supported the same pulse count. The companion is favored to be a white dwarf, but its inferred mass depends on assumptions about the pulsar’s mass and the orbit’s viewing angle.

Young explorerA pulsar is a spinning star whose signals reach us like regular flashes. When we miss lots of flashes, counting them can get tricky. Scientists made a computer tool that worked out the missing counts for one pulsar and traced its path around a companion. They think the companion is a white dwarf, but that is not certain.

Probing Solar-Wind Structure During Crab Pulsar Conjunctions with Dispersion and Faraday Rotation

Huiyu Xiao, Daniel Baker, Thierry Serafin Nadeau+3 more

• Instrumentation and Methods for Astrophysics
• Solar and Stellar Astrophysics

AstronomerCHIME observations of the Crab pulsar during the 2022–2026 solar conjunctions trace inner-solar-wind plasma through dispersion measure (DM) and rotation measure (RM). The scattering-corrected 2025 DM series contains a secondary enhancement on 21 June, about one week after the main conjunction peak, with ΔDM = (3.95 ± 0.20) × 10^-3 pc cm^-3, approximately 20 times the day-to-day scatter outside conjunction. Ionosphere-corrected RM measurements, formed by combining each observation’s single pulses, show excursions up to roughly 60 rad m^-2. Their sign changes are consistent with heliospheric magnetic-sector boundary crossings. No RM counterpart is found for either the secondary 2025 DM enhancement or a similar post-conjunction DM tail in 2026. Slopes of RM excess versus DM excess yield estimates of the electron-density-weighted line-of-sight magnetic field: for sectors with significant slopes, the reported lower limits on its magnitude span approximately 0.2–10 mG near conjunction, with the largest values in 2025.

PublicAs the Crab pulsar appeared close to the Sun in the sky, its radio signals passed through the inner solar wind, allowing researchers to study the charged gas there. CHIME observations from 2022–2026 measured both signal delays, which trace electrons along the path, and changes in polarization, which also depend on the magnetic field. In 2025, an extra electron-related signal appeared about a week after the main peak, standing out at about 20 times the usual day-to-day scatter outside this period. Neither this feature nor a similar lingering signal in 2026 had a matching polarization-rotation feature. Changes in the sign of the polarization rotation are consistent with the signal path crossing boundaries between solar-wind magnetic regions. Combining the two measurements, the researchers estimate the magnetic-field component along the signal path, weighted toward electron-rich gas; the strongest estimates occur in 2025.

Young explorerA star called the Crab pulsar sends us radio pulses. When it looks close to the Sun in our sky, those pulses travel through gas blowing away from the Sun. Scientists watched how the gas delayed and changed the pulses. In 2025, they saw an extra bump in the delay after the biggest bump. But another clue, a change in how the radio waves were turned, had no matching bump. Together, these clues help scientists estimate part of the magnetic field in the Sun’s flowing gas.

Can Magnetic Reconnection Accelerate Energetic Particles in the Heliosheath?

Jeongbhin Seo, Teresa Boland, Fan Guo+2 more

• Solar and Stellar Astrophysics

AstronomerThe study models compression-driven energetic-particle acceleration during magnetic reconnection in the heliospheric current sheet using an MHD–SDE framework with particle feedback on the MHD evolution. Under the heliosheath conditions considered, acceleration is inefficient downstream of the termination shock. Reconnection near the heliopause generates stronger compression and a differential intensity spectrum J(ε) ∝ ε^-5.4. Even this hardest simulated spectrum is substantially steeper than the typical observed heliosheath spectrum, J(ε) ∝ ε^-1.5. The results indicate that reconnection alone cannot explain heliosheath energetic-particle acceleration under the modeled conditions.

PublicWhat gives particles their high energies in the outer reaches of the Sun’s domain remains debated. This study uses simulations to test whether magnetic reconnection—the rearrangement of magnetic fields—can accelerate particles through compression. For the conditions tested, acceleration is weak downstream of the termination shock. It is stronger near the heliopause, the outer boundary of the heliosphere, but the simulated particle intensity still falls with energy much faster than observations show. The results suggest that magnetic reconnection alone is not enough to explain the energetic particles in this region.

Young explorerFar from the Sun, tiny particles move very fast, and scientists are still figuring out how they get that way. The researchers used a computer model to see whether magnetic fields changing shape could squeeze the particles and speed them up. This worked better near the outer edge of the Sun’s space bubble, but the model still had too few very energetic particles compared with what scientists observe. For the conditions they tested, this process does not seem to explain the particles all by itself.

Energetic Nonthermal Electrons within the Above-the-looptop Regions in Solar Flares: Acceleration, Feedback, and Quasi-Periodic Pulsations

Jeongbhin Seo, Fan Guo, Xiaocan Li+3 more

• Solar and Stellar Astrophysics

AstronomerThe authors introduce a numerical method coupling magnetohydrodynamics and energetic particles, including feedback from nonthermal electrons, to study flare electron acceleration and transport. In the simulations, a large fraction of energetic electrons are accelerated in current-sheet and termination-shock regions, and most concentrate above the looptop, carrying a sizable share of the released energy. Stronger nonthermal-electron feedback produces steeper energy spectra. Periodic impacts of magnetic islands on the above-the-looptop region drive oscillations in nonthermal-electron energy density, offering a possible explanation for observed quasi-periodic pulsations rather than establishing their origin.

PublicSolar flares release magnetic energy and accelerate electrons to high energies. In some flares, many of these energetic electrons occupy a region just above the tops of magnetic loops. The researchers developed a computer simulation that includes how these electrons affect the surrounding magnetized gas. In the simulations, many electrons gain energy in a current sheet and at a termination shock, and most energetic electrons gather above the loops, carrying a substantial share of the released energy. Stronger electron feedback makes the highest-energy electrons relatively less common. Repeated impacts by magnetic islands cause the electrons' energy density to rise and fall in the model, which might help explain the rhythmic pulses observed in flares.

Young explorerA solar flare is a big burst of energy on the Sun. Scientists made a computer model to explore how tiny particles called electrons get lots of energy. In the model, most of the speedy electrons gather just above the tops of magnetic loops. Little magnetic islands bump into that area again and again, making the energy packed into the electrons rise and fall. This might help explain why real flares sometimes pulse, but the model does not prove that is the reason.

Constraining the white-dwarf mass in the intermediate polar IGR J17014-4306 using X-ray and optical spectroscopy

D.C. Souza, M.P. Diaz, A.S. Oliveira+7 more

AstronomerA joint NuSTAR, XMM-Newton, and Swift spectral analysis of the intermediate polar IGR J17014-4306, using a multi-temperature cooling-flow model, yields a maximum post-shock temperature of 50 keV (+11/-8) and an inferred white-dwarf mass of 0.94 solar masses (+0.09/-0.07). An independent fit of the NuSTAR spectrum above 10 keV with ipolar30KK gives 0.88 solar masses (+0.14/-0.12). Time-resolved SOAR optical spectroscopy measures a donor radial-velocity semi-amplitude of 165 ± 4 km/s and a mass function of 0.249 ± 0.018 solar masses. Combining these constraints with eclipse geometry and the X-ray-derived white-dwarf mass favors a donor-to-white-dwarf mass ratio of approximately 0.76–0.95 and a donor mass of approximately 0.67–0.89 solar masses. The limiting case q = 1 gives a white-dwarf mass upper limit of 1.14 solar masses. The results indicate a relatively massive white dwarf, but no independent dynamical white-dwarf mass is available to establish whether the X-ray estimates agree with dynamics or underestimate the mass.

PublicResearchers studied the magnetic white-dwarf binary IGR J17014-4306 using X-ray observations and optical measurements of its companion star’s motion. Two X-ray models estimate the white dwarf’s mass at about 0.9 times the Sun’s mass, with uncertainties. Combining these model-based estimates with the companion’s motion and the system’s eclipse geometry suggests that the companion has roughly 0.67–0.89 times the Sun’s mass. The results point to a relatively massive white dwarf. However, the optical observations do not provide an independent measurement of its mass, so they cannot yet establish whether the X-ray estimates are accurate or too low, as has been found in other systems of this type.

Young explorerScientists watched two stars that circle each other. One is a small star called a white dwarf. They studied X-rays and watched how its partner moved to learn how heavy the stars might be. Their estimates suggest the white dwarf is quite heavy, but they still need a separate way to check its weight.

Gravitational-Wave Constraints on R² Gravity

Pawan Kumar Gupta, Laura Sagunski

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThe authors map quadratic f(R) = R + aR² gravity onto an effective-field-theory inspiral waveform for generic massive scalar-tensor gravity, deriving a theory-specific phase correction controlled by a. Bayesian analyses of the binary-neutron-star events GW170817 and GW190425 yield a combined bound a ≲ 6.2 × 10^6 m² at 90% credibility, corresponding to a scalar-mass lower bound m_s ≳ 3.2 × 10^-11 eV. These are constraints within the modeled theory, not a detection of a scalar contribution. The authors report the strongest astrophysical constraint on this coupling, improving the previous best bound by approximately five orders of magnitude.

PublicResearchers used gravitational-wave signals from two neutron-star mergers, GW170817 and GW190425, to test a simple extension of Einstein’s theory of gravity. The alternative theory adds a massive scalar component whose limited range could change how the stars spiral together and the waves they emit. By modeling those changes and comparing with the signals, the team constrained the strength-setting parameter to about 6.2 million square meters or less at 90% credibility. In this theory, that corresponds to a scalar mass of at least about 3.2 × 10^-11 electronvolts. This is a limit on a possible departure from Einstein’s theory, not a discovery of one. The authors report that their astrophysical limit is roughly 100,000 times tighter than the previous best.

Young explorerWhen two neutron stars spiral together, they make tiny ripples in space. Scientists studied ripples from two pairs of these stars to check an idea about gravity. The idea adds something extra that could change the ripples, but only over a limited distance. The scientists worked out how much room the signals leave for that extra effect. They did not discover it; they set a much tighter limit on how strong it could be.

Investigating the Circumnuclear Medium of Tidal Disruption Events with Radio Observations

Chang Zhou, Wei-Hua Lei, Xiangli Lei+3 more

AstronomerThe authors compile 53 tidal disruption events (TDEs) with radio observations and derive predicted closure relations linking the temporal and spectral indices of synchrotron emission for arbitrary circumnuclear-medium density profiles and different outflow dynamical phases. Applying these relations to 26 radio TDEs with sufficiently good data, they constrain the surrounding density profiles. The constraints are generally consistent with estimates from the equipartition method, supporting closure-relation analysis as an efficient probe of the environments of quiescent supermassive black holes. Such profiles can provide diagnostics of past accretion activity.

PublicWhen a star is torn apart by a supermassive black hole, the event can launch material into the surrounding gas, producing radio emission. This study uses how that emission changes over time and across radio frequencies to investigate how the gas density varies around otherwise quiet black holes. The researchers collected 53 events with radio observations, derived theoretical relationships for different surrounding gas profiles and stages of outflow motion, and used the 26 events with sufficiently good data to constrain their gas density profiles. The results generally agree with estimates from another method, suggesting that this approach can help investigate black holes’ surroundings and past feeding activity.

Young explorerWhen a huge black hole tears a star apart, some material can rush outward into nearby gas and make radio signals. Scientists studied how those signals change to work out how thick the gas is in different places around the black hole. They gathered radio observations of 53 star-tearing events, and 26 had good enough information for this test. Their answers mostly agreed with another way of figuring it out.

Accretion-powered flares from black hole-disk collisions in galactic nuclei

Joaquin Pelle, Kyohei Kawaguchi, Masaru Shibata+1 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present radiative post-processing of relativistic hydrodynamic simulations of black hole–disc collisions, incorporating prescriptions for shock heating, eikonal optical depths, and photon escape with trapping and diffusion. Within the explored parameter range, the predicted emission is dominated by sustained accretion onto the secondary, supplied at highly super-Eddington rates, rather than cooling unbound ejecta. Predicted luminosities are typically near the secondary’s Eddington luminosity and can reach several times it, with predominantly soft X-ray emission. Lower collision velocities yield brighter flares; disc surface density mainly affects spectral evolution, with low-density discs producing roughly keV-peaked emission with weak evolution, and high-density discs producing softer early emission followed by hardening. A simulation-calibrated depletion-time estimate suggests hours-to-days durations for intermediate-mass secondaries and a proportionality between flare duration and QPE period. Implications for QPE-like transients and OJ 287 are discussed, not established observationally. Because radiative feedback on the gas is omitted, the luminosities are baseline estimates of available radiative power.

PublicThis study models the flashes that could occur when a black hole collides with a disc of gas in a galactic nucleus. The researchers calculate how radiation might escape from simulated collisions; these are predictions, not observed flashes. Their models suggest that most of the light comes from gas continuing to feed the colliding black hole, rather than from expelled gas cooling down. The predicted flashes shine mainly in soft X-rays. Slower collisions produce brighter flashes, while the amount of gas per unit disc area chiefly changes how the spectrum develops: denser discs begin with lower-energy emission that shifts to higher energies over time. An estimate based on the models suggests flashes lasting hours to days for intermediate-mass black holes, with longer flare durations associated with longer periods between quasi-periodic eruptions, or QPEs. The authors discuss possible connections to QPE-like events and OJ 287 without confirming them. The calculations omit how radiation changes the gas, so their brightness estimates represent available power rather than firm predictions of actual brightness.

Young explorerA black hole crashing through a big disc of gas might make a bright flash. Scientists used computer models to work out what that flash could look like; they did not watch one happen in this study. The models suggest that most of the light comes from gas feeding the black hole after the crash, not from gas flying away. Much of that light would be X-rays, which our eyes cannot see. Slower crashes made brighter flashes in the models. But the models leave out how the light pushes or heats the gas, so the real flashes could be different.

IceCube Real-time Searches for High-energy Neutrinos Coincident with LIGO/Virgo/KAGRA Gravitational-Wave Alerts in O4a

IceCube Collaboration, R. Abbasi, M. Ackermann+97 more

AstronomerAn IceCube search tested for high-energy neutrino counterparts to 85 significant and 945 low-significance compact-binary gravitational-wave candidates reported in real time by LIGO-Virgo-KAGRA during O4a and its preceding engineering run, using a ±500 s window. An unbinned maximum likelihood analysis covered significant alerts, while a Bayesian analysis incorporating astrophysical priors covered all alerts. Extended-duration searches also targeted two candidate neutron star–black hole mergers and one low-significance event with a possible subthreshold gamma-ray counterpart. No individual event showed statistically significant neutrino emission. The smallest pre-trials p-values were 0.0079 for S231029y in the likelihood search, 0.0076 for S230904n among significant Bayesian-search events, and 0.0011 for S231025a among low-significance Bayesian-search events; their post-trials values were 0.752, 0.9996, and 0.678, respectively. The Bayesian population p-value was 0.55. Event-specific upper limits were set on time-integrated neutrino flux and emitted neutrino energy, assuming isotropic emission. Pipeline improvements, including automated notices, made the median IceCube real-time response 2.7 times faster than in the previous observing run.

PublicMergers of compact objects are predicted to produce high-energy neutrinos, but this search found no statistically significant evidence of them. Researchers used IceCube data to look for neutrinos arriving within 500 seconds before or after 85 significant and 945 less-certain gravitational-wave candidate events reported by LIGO-Virgo-KAGRA. They also searched for longer-lasting emission from three selected candidates. Two statistical approaches found no convincing individual association, and a test of the population found no significant signal either. The results place upper limits on the neutrino output of each event, assuming that emission spreads equally in all directions; they do not establish that the mergers emitted no neutrinos. Improvements to the alert system made IceCube’s typical real-time response 2.7 times faster than during the previous observing run.

Young explorerWhen very dense objects crash together in space, they might send out tiny particles called neutrinos as well as ripples in space. Scientists used a detector called IceCube to look for these particles around the times of many possible crashes. They did not find a clear sign that any of the crashes sent neutrinos toward us. That does not mean there were none. The scientists used the search to work out limits on how much could have been sent out, if the particles spread equally in every direction. They also made their alert system faster.

Inferring Properties of Rotating Core-Collapse Supernovae with Gravitational-Wave Detector Networks

Almat Akhmetali, Y. Sultan Abylkairov, Solange Nunes+3 more

• Cosmology and Nongalactic Astrophysics
• Instrumentation and Methods for Astrophysics

AstronomerThis study evaluates how current and future gravitational-wave detector networks could constrain rapidly rotating core-collapse supernovae through core-bounce and early post-bounce signals. Deep-learning methods estimate peak frequency, rotation rate, and signal amplitude from noisy detector data. The analysis finds improved parameter recovery and sky coverage with detector networks. Estimated current-generation reach is about 15 kpc for peak-frequency recovery and beyond 100 kpc for rotation-rate recovery; third-generation observatories are projected to extend these distances by roughly a factor of three to four. These are performance estimates, not detections: gravitational waves from core-collapse supernovae remain undetected.

PublicGravitational waves from a collapsing star could reveal what happens deep inside it, but no such signal has yet been detected. This study uses deep learning to assess how groups of present and future detectors could measure signals from rapidly spinning stellar cores as they collapse and bounce. The analysis finds that detector networks improve both the recovery of signal properties and coverage of the sky. For current-generation networks, it estimates that a signal's peak frequency could be measured out to about 15 kiloparsecs, while the core's rotation rate could be recovered beyond 100 kiloparsecs. Future third-generation observatories are predicted to extend those ranges by roughly three to four times. These estimates describe potential capabilities, not observations of an actual supernova signal.

Young explorerWhen the middle of a big star falls inward and bounces, it may make tiny ripples in space. Scientists have not caught these ripples from a collapsing star yet. In this study, they used a computer learning method to explore how teams of ripple detectors could tell how fast the star's middle was spinning. Their work suggests that detectors working together could do better, and future detectors could study stars farther away. That is a prediction, not something they have seen happen yet.

A unified modeling of X-ray and gamma-ray spectro-polarimetric data: the case of Cygnus X-1

Tristan Bouchet, Thomas Siegert, Victoria Grinberg+4 more

AstronomerThe authors present a broadband spectro-polarimetric framework that jointly fits spectra and polarization from independent instruments, accommodating different energy binning, statistical significance, and energy-dependent polarization mixing among model components. Applied to Cygnus X-1 across 2 keV–2 MeV, it improves characterization of the soft gamma-ray hard tail and constrains the optically thin synchrotron cutoff energy to (2.8 +0.6/−0.8) × 10² keV. They discuss implications for non-thermal electron acceleration in the context of Bohm diffusion and synchrotron cooling. Magnetic-field helicity combined with Doppler boosting is proposed, not established, as an explanation for the observed polarization misalignment.

PublicObservations of black hole systems such as Cygnus X-1 show patterns in high-energy light that challenge current models. The authors introduce a way to combine measurements of the light’s energy distribution and polarization—its preferred orientation—from different instruments. Applying it to Cygnus X-1 improves their description of its high-energy emission and places the cutoff energy of a modeled synchrotron component near 280 keV, with an uncertainty of +60/−80 keV. They discuss what this could mean for how electrons gain and lose energy. They also propose that a twisting magnetic field and changes in apparent brightness caused by motion could explain an observed mismatch in polarization directions; this explanation is not yet established.

Young explorerScientists studied very energetic light from a system with a black hole. They made a new way to put together clues from different tools, including how much light there is and which way its waves line up. This helped them better describe part of the light from a system called Cygnus X-1. They also suggested that a twisting magnetic field and moving material might explain why some light waves line up differently, but that idea is not proven.

Correlated Signatures of Plasma Lensing in Fast Radio Bursts

Paz Beniamini, Pawan Kumar

AstronomerThis theoretical study derives correlated diagnostics for a one-dimensional Gaussian plasma lens near a fold caustic, rather than identifying lensing in an observed FRB. It distinguishes image phase separation from observable group-delay difference and treats resolved copies, overlapping images with negligible mutual coherence, and coherent spectral interference separately. The model links magnification, image delay, spectral-envelope width, fringe spacing, differential dispersion, caustic curvature in time-frequency space, and the third image’s brightness and ordering. Separate source-size constraints follow from large fold magnification and fringe visibility; high-contrast fringes also constrain mutual coherence and, after accounting for the observed spectrum and instrumental bandpass, intrinsic radiation coherence. The study relates the wave-optics magnification scale to lens plasma column and derives conditions for differential Faraday rotation. Its analysis suggests that clean lensing by volume-filling turbulence requires fine tuning, favoring sparse structures as candidates. Convincing identification still requires multiple correlated observables to match one lens model.

PublicClouds of charged particles have been proposed as lenses that could reshape fast radio bursts, producing repeated copies or patterns across radio frequencies. But those features can have other explanations. This theoretical study works out how several clues should fit together for one particular lens model, including burst brightness, arrival-time differences, and interference patterns. Such patterns could also constrain the emitting region’s size and the coherence of its radio waves, provided the measured spectrum and instrument response are accounted for. The analysis suggests that isolated sheets, filaments, boundaries, or shocked clumps may be more promising lenses than turbulence filling an entire region. It provides consistency tests for the lensing explanation, not an observational confirmation.

Young explorerA cloud of tiny charged particles might bend a quick flash of radio waves, making it look copied or striped. Scientists used a math model to work out which clues should appear together if that happens. This does not prove a cloud made those patterns: other things could make them too.

Direction-of-arrival estimation of a gravitational wave by correlations between quadrupole moments of pulsar timing data

Taichi Ueyama, Hodaka Tamura, Hideki Asada

• General Relativity and Quantum Cosmology
• High Energy Physics - Theory

AstronomerThis paper develops a method for estimating gravitational-wave arrival direction from pulsar timing arrays, considering a dominant isolated source, such as a supermassive black hole binary, over an isotropic stochastic background. As a possible alternative to matched filtering, it uses correlations between quadrupole moments of the timing data. The authors show that these correlations form a three-dimensional traceless matrix of rank 3, closely related to a gravitational-wave projection tensor, from which the arrival direction can be estimated without a template bank or an a priori Gaussian-noise assumption. They replace pulsar averaging with a celestial-sphere mean and use Voronoi-derived area weights to account for nonuniform pulsar sky coverage. Direction-estimation errors are also examined in anticipation of the Square Kilometre Array. The abstract presents a methodological demonstration, not an observed source localization.

PublicThe paper explores a way to find where a gravitational wave comes from using its effects on the timing of pulsar signals. It considers a dominant individual source, possibly a pair of supermassive black holes, against a background of gravitational waves. The proposed method extracts directional information from correlations in patterns across the timing data, without requiring a bank of predicted signal templates or assuming Gaussian noise. It also weights different parts of the sky to account for uneven pulsar coverage. The authors examine direction-finding errors with the future Square Kilometre Array in mind, but the abstract does not report locating an actual source.

Young explorerPulsars send signals that act like ticking clocks in space. A passing ripple in space can change when those ticks reach us. These scientists worked out a way to use patterns in the changes to estimate which direction a strong ripple came from. This is a method, not a report of finding a real ripple's home.

Accurate waveforms for generic planar-orbit binary black holes: The multipolar effective-one-body model SEOBNRv6EHM

Aldo Gamboa, Alessandra Buonanno, Lorenzo Pompili+8 more

• General Relativity and Quantum Cosmology

AstronomerThe authors present SEOBNRv6EHM, a time-domain effective-one-body waveform model for compact binaries on generic planar orbits, calibrated to quasi-circular SXS numerical-relativity simulations. It includes the (2,2), (2,1), (3,3), (3,2), (4,4), and (4,3) modes through inspiral, merger, and ringdown, and also models dynamical captures and scattering encounters. Novel resummations are applied to radiation reaction and waveform modes. Validation uses 592 quasi-circular, 319 eccentric, one dynamical-capture, and two scattering waveforms, plus scattering-angle comparisons with 61 simulations. Accuracy is comparable to SEOBNRv5 models for quasi-circular and low-eccentricity binaries. For highly eccentric systems, the authors report waveform mismatches below or near 2% over total masses of 20–200 solar masses, for eccentricities up to approximately 0.9 evaluated 14 periastron passages before merger. Reported generation times are 2–8 times faster than other state-of-the-art eccentric EOB models. These are simulation-based validation results, not measurements of observed binaries.

PublicThe study introduces SEOBNRv6EHM, a computer model that calculates gravitational waves from pairs of compact objects moving in a shared plane. It handles nearly circular and strongly elongated orbits, mergers, and encounters in which objects become bound or scatter apart. Modeling elongated orbits matters because they can provide clues to how a pair formed, and ignoring them can bias estimates of its properties. The researchers tested the model against detailed numerical simulations, rather than observed gravitational-wave signals. For highly elongated orbits, they report waveform differences below or near 2% by their comparison measure across systems totaling 20–200 times the Sun’s mass, with eccentricities reaching about 0.9 at a specified stage before merger. Accuracy for nearly circular orbits is similar to earlier models, while waveform calculations are reported to run 2–8 times faster than other leading models for eccentric binaries.

Young explorerWhen two very small, heavy objects move around each other, they make ripples in space. Scientists made a new computer model to work out what those ripples should look like, even when the objects follow very stretched-out paths or rush past each other. They checked it against detailed computer simulations, not real signals from space. It matched the simulations well, including some tricky stretched-out paths, and made its ripple predictions faster than other models they compared it with.

Neutron star cooling with medium-modified Urca rates

B. X. Zhou, J. B. Wei, Z. H. Li+2 more

• Nuclear Theory

AstronomerThe authors investigate how in-medium changes to elementary cooling processes affect observable properties of isolated neutron stars. They infer mass distributions compatible with their cooling analysis and compare them with current theoretical models. Within this analysis, current cooling data require direct Urca cooling, moderated by proton superfluidity, in most neutron stars, with its onset threshold below canonical neutron-star masses. Under that condition, medium modifications to modified Urca rates are practically insignificant, whereas neutron–neutron bremsstrahlung plays a dominant role. These conclusions are inferences from the cooling analysis, not direct observations of the individual processes.

PublicThe researchers examine how processes inside isolated neutron stars affect their cooling, and infer which distributions of stellar masses fit the cooling data. Their analysis indicates that most neutron stars need a rapid cooling process called direct Urca, partly restrained by protons being in a superfluid state. This process would need to begin at masses below the usual benchmark for neutron stars. In that case, changes caused by the surrounding matter would have little effect on a related process called modified Urca, while neutron–neutron bremsstrahlung would play a leading role. These are interpretations of cooling data rather than direct detections of those internal processes.

Young explorerThe researchers studied how neutron stars cool down when they are on their own. Their calculations suggest that most need a fast way to cool, with something inside slowing it down a bit. They also worked out which star masses could fit what we see. We cannot watch these cooling processes directly inside the stars, so the scientists use the cooling clues to figure out what may be happening.

IceCube data for astrophysical neutrinos exhibit q-statistical behavior

Constantino Tsallis, Ugur Tirnakli

• Statistical Mechanics
• High Energy Physics - Phenomenology

AstronomerAn analysis of recent IceCube astrophysical-neutrino data finds that q-Gaussians satisfactorily describe the spectra across the full measured energy interval, as reported for cosmic rays and proton-proton LHC collisions. The inferred momentum-distribution nonadditive index is q ≃ 1.6, corresponding to q_energy ≃ 1.3, compared with approximately 1.2 for cosmic rays and 1.1 for LHC data. The authors interpret these indices as indicating very-long-range space-time correlations and as reinforcing evidence for the relevance of nonadditive entropies to black holes and related cosmological phenomena, including dark energy. These broader connections are interpretations; the underlying physical mechanisms remain unresolved.

PublicThe researchers analyzed IceCube data on neutrinos from space and found that a mathematical curve called a q-Gaussian describes their energy spectrum well throughout the measured range. Similar descriptions have been reported for cosmic rays and proton collisions at the LHC, but the IceCube fit has a larger value of the parameter used to characterize nonadditive statistics. The authors interpret this as a sign of connections extending over very large distances and times. They also suggest it strengthens the case for using nonadditive descriptions of entropy in studying black holes and phenomena such as dark energy. The fit does not establish those broader links, and the physical explanation remains an open question.

Young explorerScientists looked at measurements of tiny particles called neutrinos coming from space. A special math curve matched how their energies were spread out. The scientists think this pattern might be a clue that things very far apart in space and time are connected. They still do not know what would make those connections happen.

Brewing another binary in the Teapot: Nandou=Phi Sagittarii

Idel Waisberg, Boaz Katz

• Astrophysics of Galaxies

AstronomerCombining VLTI/GRAVITY with archival spectroscopy, radial velocities and photometry, the authors determine the orbit of Nandou (Phi Sagittarii): P = 238.844 ± 0.011 days, a = 1.32 ± 0.10 au and e = 0.418 ± 0.004. Dynamical masses of 3.8 ± 0.9 and 1.6 ± 0.4 solar masses are limited chiefly by the parallax uncertainty (12.5 ± 1.0 mas). The 1997 Hipparcos intermediate astrometric data are consistent with the expected approximately 5 mas photocenter semimajor axis, whereas the 2007 reduction gives 1.7 ± 0.3 mas. The authors interpret this discrepancy as evidence that overly aggressive satellite-attitude modeling can suppress orbital motion through overfitting. Comparing the primary's temperature of 12,000 ± 250 K and radius of 5.1 ± 0.4 solar radii with evolutionary models suggests an approximately 4-solar-mass star near the end of the main sequence. Its eventual evolution into a symbiotic star is a likely prediction, not an observed outcome.

PublicNandou, also called Phi Sagittarii, is a pair of stars in Sagittarius whose orbit the researchers determined by combining several kinds of observations. The stars circle each other about every 239 days along an elongated orbit. Their estimated masses are roughly four and one-and-a-half times the Sun's mass, but uncertainty in their distance limits the precision. The study also finds that a revised version of Hipparcos satellite data shows less orbital motion than expected; the authors attribute this to data modeling that removed some of the real motion. Comparing the larger star's temperature and size with models suggests that it is nearing the end of its main-sequence life. The authors predict that Nandou will most likely eventually become a symbiotic star system, rather than reporting that this has already happened.

Young explorerNandou looks like one star, but it is really two stars going around each other. Scientists used several kinds of observations to work out their path. One trip takes about 239 days. They also found clues that an older way of working with satellite measurements kept the stars' motion better than a newer way. By comparing the bigger star with models of how stars grow older, they think it is getting close to the end of one long part of its life. That is their best explanation, not something they watched happen.

The spatial structure of solar magnetoconvection at scales up to 60 Mm

D. Przybylski, R. H. Cameron

AstronomerA MURaM small-scale dynamo simulation, extending 50 Mm below the solar surface across a 60 Mm horizontal domain, investigates radial and horizontal convection at mesogranular and supergranular scales. Its resolution begins to resolve magnetic bright points in intergranular lanes. At all resolved scales, simulated flow amplitudes agree with those inferred from Doppler and local correlation tracking measurements. The analysis indicates that near-surface density perturbations influence vertical Doppler-velocity power at supergranular and larger scales. The mode structure at depth is broadly consistent with the cited earlier study, but the horizontal forcing scale varies as Hρ^(2/3), rather than Hρ. The simulation reproduces observations up to 60 Mm and shows no excess power associated with the convective conundrum within its simulated range, l ≥ 70; this does not establish what happens at larger, unmodeled scales.

PublicResearchers used a computer simulation to study patterns of rising, sinking, and sideways-moving material near the Sun’s surface. The model reaches 50 Mm beneath the surface and spans 60 Mm horizontally. Across the sizes it can resolve, its simulated motions match the strengths inferred from existing observations. The analysis also indicates that density variations near the surface affect measurements of vertical motion on large scales. Within the model’s limited size range, the researchers do not find the excess strength of convection associated with a known disagreement between models and observations. This agreement does not settle the mystery of missing giant convection cells at still larger scales.

Young explorerMaterial near the Sun’s surface moves up, down, and sideways. Scientists made a pretend piece of the Sun on a computer to learn about these movements. For the sizes the computer could show clearly, the movements matched what people had measured on the real Sun. But the pretend piece was only so big, so it could not solve the mystery of the much bigger patterns scientists have not found.

How fast is the fastest-rotating O-type star in the Galaxy?

M. Curé, R. S. Levenhagen, D. Turis-Gallo+4 more

• Astrophysics of Galaxies

AstronomerThe authors reanalyse the extreme Galactic O-type runaway LAMOST J040643.69+542347.8 with an oblate, gravity-darkened Roche photosphere, fitting continuum-normalised spectra over 4000–4600 Å with ZPEKTR and masking interstellar and wind- or circumstellar-dominated features. The model reproduces He II 4200, He I 4471, and He II 4542. Inferred parent non-rotating counterpart parameters are Teff = 38,716 ± 1,041 K and log g = 4.12 ± 0.12, with projected equatorial velocity ve sin i = 587 ± 73 km/s. The central grid solution gives Ω/Ωc = 0.93, ve/vc = 0.77, i = 65°, Re/Rp = 1.25, and equatorial centrifugal-to-gravitational acceleration ratio ηe = 0.50. Thus, despite its high angular rate, this solution is not critical in equatorial force balance: Roche critical rotation requires ηe = 1 and Re/Rp = 1.5. The projected velocity is higher than, but statistically consistent with, the previous spherical-fit estimate. Assessing proximity to critical rotation requires the angular-rate, speed, and force ratios together; a controlled spherical fit using the same atmosphere grid is still needed to isolate deformation and gravity-darkening biases.

PublicA new analysis of the light from the massive, rapidly spinning star LAMOST J040643.69+542347.8 supports a flattened shape with brightness that varies across its surface. Rather than treating the star as a sphere, the researchers fitted its spectrum with a model that includes rotational distortion and gravity darkening. They infer a projected equatorial speed of 587 ± 73 kilometres per second, higher than but statistically consistent with an earlier spherical-model estimate. Their central model has an equator about 25% wider than the pole-to-centre radius. Although its angular rotation rate is 93% of the model’s critical value, the outward centrifugal acceleration at the equator is only half the inward gravitational acceleration, so this solution does not reach the critical balance. The authors caution that several measures are needed to judge how close the star is to critical rotation. A matched comparison with a spherical model is still needed to establish how much ignoring its distorted shape changes the inferred properties.

Young explorerScientists studied the light from a big star that spins very fast. They used a model that lets the star bulge around its middle instead of being a perfect ball, and lets some parts shine more brightly than others. This model matched important parts of the star’s light. In their best-fitting model, gravity still pulls inward at the star’s middle more strongly than spinning pushes outward. The scientists still need to compare models more carefully to learn how much the star’s shape changes their answers.

Photometric Study of a Distant SU UMa-type Dwarf Nova KSP-OT-201803a

Sang Chul Kim, Youngdae Lee, Dae-Sik Moon+2 more

AstronomerBVI photometry from the KMTNet Supernova Program identified one superoutburst and three normal outbursts in KSP-OT-201803a during 2018–2019, supporting its classification as an SU UMa-type dwarf nova. Phase dispersion minimization of plateau-phase superhumps gives P_sh = 127.4 minutes (0.08847 days). Stacking ten quiescent images yields V = 22.59 ± 0.18 mag; the superoutburst amplitude is 4.97 ± 0.18 mag and its duration is 16.59 days, typical of this class. Using the superhump–orbital-period relation, the authors estimate a distance of 3.7 ± 0.3 kpc, a Galactocentric distance of 9.4 kpc, and a height of +1.2 kpc above the Galactic plane. This location suggests possible halo or thick-disk membership, not a confirmed Population II identification; a different evolutionary history from Population I systems is therefore an interpretation. Assuming an orbital period a few percent shorter than the superhump period, the authors suggest that the system may recently have emerged below the dwarf-nova orbital-period gap, quoted as 2.45–3.18 hours, and resumed mass transfer. The orbital period and this evolutionary scenario are not directly established by the reported observations.

PublicAstronomers discovered a distant dwarf nova called KSP-OT-201803a by tracking its brightness over two years. They recorded one major brightening and three ordinary outbursts, identifying it as an SU UMa-type dwarf nova. During the major outburst, repeating brightness variations had a period of 127.4 minutes. The major outburst lasted about 16.6 days. Using a relationship between these brightness variations and orbital timing, the researchers estimate that the system lies 3.7 ± 0.3 kiloparsecs away and well above the Milky Way’s main plane. Its location could place it among the Galaxy’s older populations, but that membership is not confirmed. The authors also suggest it may recently have restarted transferring material after passing through a particular range of orbital periods. That explanation depends on an estimated, rather than directly measured, orbital period.

Young explorerAstronomers watched a faraway star system get brighter and dimmer. In two years, they saw one big brightening and three smaller ones. During the big one, its light repeated a pattern about every two hours. The scientists think it might belong to an old group of stars and might have started passing material between its stars again. Those ideas are not certain yet.

Frequent Optical Flares in an M-type Detached Eclipsing Binary TIC 349005337

Xiao Zhou, Liying Zhu, Wei Hu+4 more

AstronomerCombined TESS photometry and LAMOST medium-resolution spectroscopy characterize TIC 349005337 as an active, detached M-type eclipsing binary with a 2.6079133-day period. Joint light-curve and radial-velocity analysis yields primary mass and radius of 0.517 ± 0.009 solar masses and 0.518 ± 0.003 solar radii, and secondary values of 0.298 ± 0.004 solar masses and 0.357 ± 0.003 solar radii. The secondary is described as fully convective. Twelve high-energy flares are identified, the most energetic reaching 3.87 × 10^34 erg, establishing strong magnetic activity in the system. The authors interpret the frequent superflares as evidence that magnetic activity and substantial starspot coverage strongly modify atmospheric structure; this is an interpretation rather than a direct atmospheric measurement. They argue that the flares constrain distributed dynamo models in the low-mass regime and motivate studies of binary dynamics, magnetic reconnection, and possible effects on hypothetical planets' atmospheres. The abstract does not assign the flares to a particular component or report any planets.

PublicAstronomers studied two small stars that orbit each other every 2.61 days and periodically pass in front of one another. Combining TESS brightness measurements with LAMOST spectra let them determine both stars' masses and sizes. One has about 52% of the Sun's mass, while the other has about 30% and is described as fully convective. The observations revealed 12 powerful stellar flares, showing that the system is intensely magnetically active. The researchers suggest that this activity, together with extensive starspots, strongly affects the stars' atmospheric structure. They also identify the pair as a useful test of theories about how small stars generate magnetic fields. Possible consequences for the atmospheres of orbiting planets are a motivation for further work, not an observed result; no planets are reported.

Young explorerTwo small stars go around each other about once every two and a half days. Sometimes one passes in front of the other and blocks some of its light. Scientists used that changing light and other clues to work out how big and heavy the stars are. They also spotted 12 powerful flashes called flares. These flashes show that the stars have very active magnetic fields. The scientists think this activity and spots on the stars may change their outer layers, but there is still more to learn.

Collective Characterization of Polar Crown Filament Eruptions

Ying Wang Yan Xu, Ju Jing, Vasyl Yurchyshyn+1 more

AstronomerA collective analysis of 50 polar crown filament (PCF) disappearance events spanning solar cycles 24 and 25 characterizes their magnetic structure and eruption dynamics. Rotational motions occur in 24 events; nine have magnetic configurations clear enough for comparison with numerical model predictions. All nine rotate in the predicted direction, suggesting, but not establishing, magnetic-flux-rope-like structures. All but one of the 50 PCFs disappeared through eruption rather than thermal disappearance, and most associated coronal mass ejections had speeds below 800 km s−1. For events accompanied by transient coronal holes, estimated magnetic fluxes associated with dimming regions are of order 10^20–10^21 Mx. Time–distance analysis resolves a slow-rise to fast-rise transition in 22 events, at heights from several tens to about 160 Mm; the mean onset velocity is about 2.8 km s−1 after excluding the highest-velocity event.

PublicPolar crown filaments are structures on the Sun linked to magnetic fields near its poles. Their movement toward the poles helps trace the drift of magnetic fields from decayed active regions. Researchers examined 50 filament disappearance events across solar cycles 24 and 25. In all but one case, the filament disappeared by erupting rather than through a thermal disappearance. Twenty-four showed rotation, and nine had magnetic configurations clear enough to compare with computer-model predictions. All nine turned in the predicted direction, suggesting that they may have rope-like magnetic structures, though this does not prove it. Most associated coronal mass ejections were slower than 800 kilometers per second. In 22 events, the researchers clearly identified a change from slow to fast rising, occurring at heights from several tens of thousands to about 160,000 kilometers.

Young explorerNear the Sun’s poles are shapes called filaments, linked to its magnetic fields. Scientists studied 50 times when these shapes disappeared. All but one disappeared by bursting outward. Some turned as they moved. For nine that scientists could check clearly, the turning matched what a computer model predicted. That is a clue that their magnetic fields might be shaped like ropes, but it is not proof. In 22 cases, scientists could clearly see the shapes change from rising slowly to rising quickly.

Tiny Quiet-Sun EUV Ejections Revealed by High-resolution Multiwavelength Observations

Nengyi Huang, Yuqian Wei, Qin Li+2 more

AstronomerCoordinated Solar Orbiter/EUI, IRIS, SDO/AIA, and Goode Solar Telescope observations resolve two successive tiny quiet-Sun EUV ejections on 2022 October 29. A curved H-alpha thread precedes the events, with a compact multithermal Mg ii/Si iv precursor appearing 2.6–2.7 minutes before the first EUV brightening. EUI–AIA stereoscopy places the recurrent kernel near 2.2 Mm and sampled emission at approximately 0.6–4.2 Mm along inclined, locally arched structures. The first ejection has multithreaded, helical-looking strands; the second has straighter strands, with the cross-ridge separation of redshifted and blueshifted Mg ii k3 samples decreasing from 1.47 to 0.89 arcseconds. Despite these differences, both peaks have comparable emission-measure increments and estimated event-associated thermal contents of a few 10^26 erg under the same assumptions. Enhanced regional Si iv and k3 blueshifts and a shallower Mg ii central reversal persist before the second ejection. Component reconnection is a possible interpretation, not an established mechanism. The observations demonstrate low-lying jet-like EUV emission and indicate that the second event's spectra may reflect both atmospheric changes associated with the first event and additional energy input.

PublicAstronomers observed two small, successive eruptions in a quiet region of the Sun using several telescopes. A compact region containing gas at different temperatures appeared about 2.6–2.7 minutes before the first extreme-ultraviolet brightening. Views from different directions showed that the jet-like emission occurred in low structures near the solar surface. The first eruption displayed strands that looked helical, while the second had straighter strands. Despite their different appearances, the two had similar estimated thermal energies, subject to the same assumptions. Crucially, the second eruption began before the lower solar atmosphere's spectral signals had returned to their earlier state. Its appearance may therefore reflect changes associated with the first eruption as well as a fresh input of energy. A rearrangement of connections between magnetic fields could explain the events, but the observations do not establish that explanation.

Young explorerScientists watched two tiny bursts of glowing gas close to the Sun's surface. The first had strands that looked twisty, and the second had straighter strands. The gas had not gone back to how it was before when the second burst began. That means the first burst may have helped change how the second one looked. Scientists think the Sun's magnetic fields might have changed how they connect and helped make the bursts, but they are not sure.

Spectroscopic diagnostics of coronal fan loops using EIS/Hinode and AIA/SDO

Ananya Rawat, Girjesh Gupta

AstronomerEIS/Hinode spectroscopy and AIA/SDO imaging were used to diagnose plasma and wave properties along coronal fan loops. EIS EM-loci analysis resolves thermal components at 0.8–1.05, 1.2–1.4, and 1.6–1.8 MK, with temperature distributions compared against AIA DEM results. Fe XII line-ratio diagnostics indicate overdense loops with a slowly declining density profile that departs from the hydrostatic expectation. Alfvén-wave velocity amplitudes are inferred from non-thermal Fe XII line broadening. Combining these diagnostics with a previously reported coronal-footpoint magnetic field of approximately 200 G yields an estimated wave energy flux of approximately 2 × 10^7 erg cm−2 s−1. This exceeds values reported in earlier studies and could contribute to compensating radiative losses along the active-region fan loops; it is an inferred energy flux, not a direct measurement of wave heating.

PublicObservations from Hinode and the Solar Dynamics Observatory show that fan-shaped loops in the Sun’s outer atmosphere contain gas at several temperatures, ranging from about 800,000 to 1.8 million degrees. Spectroscopy distinguishes these temperature components particularly well. The loops are denser than expected, and their density changes along their lengths in a way that differs from a simple hydrostatic model. The researchers also interpreted some of the spreading of spectral lines as a sign of Alfvén waves, disturbances associated with magnetic fields. Using this interpretation and a previously reported magnetic-field strength, they estimated that the waves carry substantially more energy than reported in earlier studies. That energy could help offset energy the loops lose as radiation, although the study does not directly establish how much wave energy becomes heat.

Young explorerThe Sun has loops of very hot gas in its outer atmosphere. Scientists studied their light and found that the gas is not all the same temperature. They also found clues that waves may be traveling through the loops. Their calculations suggest these waves could carry energy that helps replace energy the gas loses as light, but they have not shown exactly how much of that wave energy warms the gas.

Magnetism among the oldest white dwarfs in the solar neighbourhood

Stefano Bagnulo, John D. Landstreet

AstronomerA new circular-polarisation survey of approximately 100 white dwarfs selected as featureless DC stars, combined with prior observations, yields a compilation of 205 objects: 24 firm detections and four marginal signals requiring confirmation. Four magnetic objects originally classified as DC have significant spectral-line contributions to their polarisation spectra. Depending on how these objects and marginal detections are treated, the inferred magnetic fraction in the DC-selected sample is approximately 10–14%. Objects without identifiable line contributions have circular polarisation no greater than approximately 2%, below that of some hotter, line-rich magnetic white dwarfs. The authors argue that this contrast is unlikely to reflect field decay: they find no significant dependence of magnetic incidence on cooling age and detect fields at cooling ages exceeding 9 Gyr. Strong spectral-line opacity is instead offered as a natural explanation for larger polarisation amplitudes. Detectable magnetism becomes more frequent with increasing stellar mass. Among stars with repeat observations, most average-mass magnetic objects show no clear polarimetric variability, while variability appears more common in the most massive objects.

PublicResearchers measured circular polarisation, a twisting property of light that can reveal magnetism, in about 100 white dwarfs selected because their spectra appeared featureless. Combining these measurements with earlier observations gave a sample of 205 stars, with 24 firm magnetic detections and four tentative signals that need confirmation. The estimated magnetic fraction is about 10–14%, depending on how tentative detections and four stars with unexpectedly strong spectral-line contributions are counted. Stars without identifiable line contributions showed polarisation of no more than about 2%, weaker than in some hotter magnetic white dwarfs. The researchers suggest that spectral lines can strengthen the polarisation signal, rather than the weaker signals necessarily indicating fading magnetic fields. They found no significant link between the frequency of magnetism and cooling age, and detected fields in stars that have been cooling for more than nine billion years. Detectable magnetism was more common at higher stellar masses. Repeated observations usually showed no clear polarisation changes in average-mass magnetic stars, while changes appeared more common among the most massive stars.

Young explorerScientists studied small stars called white dwarfs. They looked for a special twist in the stars’ light that can show whether a star is magnetic. Out of 205 stars, 24 clearly showed this twist, and four more might have it but need another check. Some stars had only a little twist. The scientists think this may be because of how the stars make their light, not because their magnets have grown weak with age. They even found magnetic stars that have been cooling for more than nine billion years! Heavier stars were more likely to show magnetism, and the twist in their light also seemed more likely to change.

Population synthesis of substellar companions surviving common-envelope evolution

Nicolas F. Miranda, Alex Mauch-Soriano, Joaquin A. Barraza-Jorquera+3 more

• Earth and Planetary Astrophysics

AstronomerThis population-synthesis study models engulfed substellar companions to predict which survive common-envelope (CE) evolution around white-dwarf progenitors. The calculations vary envelope-ejection efficiency and include either gravitational and thermal energy or the full internal-energy budget. In the models, no companions survive engulfment on the red-giant branch or early asymptotic-giant branch; survivors arise exclusively during the thermally pulsing asymptotic-giant branch, when weakly bound envelopes can permit even relatively low-mass companions to survive. Predicted survivors typically have orbital periods of a few hours. The predicted occurrence rate reaches at most 0.16% of white dwarfs, corresponding to an upper limit of 2.53 companions within 50 pc. Transit detectability is mainly geometry-limited, while all predicted survivors would produce infrared excess detectable with JWST within 50 pc. These are model predictions, not detections, and depend critically on envelope structure at engulfment, ejection efficiency, and the contribution of recombination energy to envelope removal.

PublicComputer models suggest that a small population of companions too low in mass to be stars could survive being swallowed by an expanding star and end up orbiting its white-dwarf remnant. Survival is rare in these calculations: it occurs only during a late, pulsing stage of the star’s evolution, when its outer layers can be loosely bound enough to be expelled. The surviving companions generally complete an orbit in a few hours. The models predict that at most 0.16% of white dwarfs host such survivors, equivalent to an upper estimate of 2.53 companions within about 50 parsecs. Whether a companion crosses in front of its white dwarf depends mainly on our viewing angle, but the study predicts that JWST could detect the extra infrared light from every modeled survivor within that distance. These are predictions rather than discoveries, and they depend strongly on how the star’s outer layers are structured and how much energy is available to throw those layers off.

Young explorerWhen an old star grows big, it can swallow a little companion that is too small to be a star. Scientists used computer models to ask whether the little companion could survive. In their models, almost all did not. A few survived when the star was very old and its outside layers were easier to push away. Those survivors would race around the leftover white dwarf in just a few hours. The scientists predict that a special telescope called JWST could spot their extra infrared light if they are close enough to us. They have not found these companions in this study; the computer models predict what might be there.

The formation and evolution of Wolf-Rayet stars with temperature-dependent winds

Guy O. Flint, Avishai Gilkis, Tomer Shenar+1 more

• Astrophysics of Galaxies

AstronomerThis modeling study incorporates recent theoretical, temperature-dependent Wolf-Rayet (WR) mass-loss prescriptions into single and binary stellar evolution calculations at Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud (SMC) metallicities. The prescriptions derive from hydrodynamically consistent atmosphere calculations and depend strongly on temperature at the wind-launching region. The resulting winds can substantially alter evolution near the WR-formation threshold. In particular, transitioning from a hydrogen-rich WNL prescription to a classical WR wind driven by the hot iron opacity bump makes some SMC-metallicity models remain at approximately 70–90 kK for an extended period. This creates a model concentration in the temperature range occupied by most observed SMC WR stars, a previously difficult feature to reproduce. The results support improved agreement with observed populations, but WR wind implementation remains an important modeling uncertainty.

PublicWolf-Rayet stars lose mass through powerful winds, but how to represent those winds remains a major uncertainty in models of stellar evolution. This study tested theoretical wind descriptions in computer models of single stars and stars in pairs, using chemical compositions characteristic of the Milky Way and two nearby galaxies. The new descriptions make mass loss strongly dependent on temperature where the wind begins. With one particular transition between wind descriptions, some models with the Small Magellanic Cloud’s chemical composition stayed for longer at about 70,000–90,000 kelvin. Most observed Wolf-Rayet stars in that galaxy occupy this temperature range, which earlier models had struggled to explain. The study therefore improves the match between models and observations; it does not directly measure the stars’ winds or establish that this wind description is definitive.

Young explorerSome very big stars blow strong winds that carry away some of their material. Scientists used computer models to see how these stars might change when their winds depend on how hot they are. In some models, the stars stayed hot—but not at their hottest—for longer. Their temperatures then matched those of many real stars of this kind in a nearby galaxy. That is a helpful clue, but scientists are still working out exactly how the winds work.

The Space-Based Time-Domain Revolution in Astrophysics

Daniel Huber

• Earth and Planetary Astrophysics
• Astrophysics of Galaxies
• High Energy Astrophysical Phenomena
• Instrumentation and Methods for Astrophysics

AstronomerThis review surveys the impact of space-based time-domain photometry from CoRoT, Kepler/K2 and TESS over the past two decades. Continuous, high-cadence, high-precision light curves for millions of Galactic and extragalactic sources have enabled advances well beyond exoplanets. Highlights include probing stellar interiors and convection, linking rotation to magnetic activity, characterizing young-star variability, using stellar-population ages to investigate Milky Way formation, and detecting dark compact-object populations through binary variability. Early observations of explosive transients inform supernova progenitor studies, while quasi-periodic galaxy variability probes accretion onto supermassive black holes and stellar tidal disruption. Solar system applications include inferring asteroid compositions from rotation periods and amplitudes, constraining ice-giant cloud structure, and discovering outer solar system objects. These are reviewed observational advances and diagnostic interpretations, rather than newly reported measurements. Open data and software have also supported high scientific productivity and citizen-science discoveries.

PublicSpace telescopes such as CoRoT, Kepler/K2 and TESS have repeatedly measured the brightness of millions of objects with exceptional precision. This review explains how those changing-light records have transformed much more than the search for planets. They help astronomers investigate the insides of stars, their rotation and magnetic activity, and the history of our galaxy. Brightness changes in paired stars can also reveal otherwise dark companions, including black holes and neutron stars. Observations of the beginnings of stellar explosions offer clues about the stars that exploded, while roughly repeating changes in galaxy light help researchers study matter falling toward giant black holes and stars being torn apart. Closer to home, the data provide clues to asteroid composition and ice-giant clouds and have enabled discoveries in the outer solar system. The review also highlights how public data and software let citizen scientists discover planets and unusual stellar behavior.

Young explorerSome space telescopes watch how things in the sky get brighter and dimmer. This review tells how those changes help scientists learn what is inside stars, how stars spin, and what happens when stars explode. They also give clues about dark objects called black holes, clouds on faraway planets, and rocky asteroids. The telescopes share their information, so people who are not professional scientists have helped find new planets and stars whose light changes in unusual ways.

Moment-based formulas for the transport coefficients

J.-F. Wang, G. Qin

• Fluid Dynamics

AstronomerThis theoretical study investigates variable-dependent diffusion coefficients in transport equations relevant to astrophysics and plasma physics. For momentum transport, the authors relate the coefficients to statistical quantities, including some new ones, and derive logarithmic forms that differ from previous results. They also obtain a logarithmic formula for isotropic pitch-angle scattering. For fractional transport equations, they derive coefficients expressed in terms of moments directly from the governing equations. The abstract reports mathematical results rather than observational or experimental tests.

PublicThe paper studies mathematical equations used to describe how particles move and spread in space and in plasmas. It focuses on diffusion coefficients—quantities that describe spreading and can vary with other variables. The authors connect these coefficients to statistical descriptions of motion and derive formulas involving logarithms that differ from earlier results. They also derive formulas for two other transport settings. These are theoretical findings; the abstract does not report measurements testing them.

Young explorerImagine tiny particles moving around and spreading out. Scientists use math rules to describe that motion. This paper works out formulas for parts of those rules, using numbers that describe the particles as a group. Some formulas look different from ones found before. This is math work, not a report of watching particles in an experiment.

A breath of fresh air: Oxygen enhancement from silicate sublimation during early protostellar evolution

F.J. Ballieux, M.K. McClure, Ł. Tychoniec+5 more

• Earth and Planetary Astrophysics

AstronomerJWST MIRI and NIRSpec observations of the Class I protostar HOPS-68 reveal absorption by SiO, H2O, CO2, and 13CO. LTE slab modeling places the absorbing gas in a 300–500 K layer above the hot disk midplane, spanning 0.3–16 AU and blueshifted by 33–53 km/s relative to the system. ALMA observations separately resolve an SiO-rich jet and wind kinematically. Combining these findings with previously detected crystalline silicates, the authors conclude that HOPS-68 is undergoing refractory recondensation analogous to that identified in HOPS-315 and to the Solar System’s meteoritic t=0 epoch. They interpret the absorbing layer as the base of a disk wind carrying sublimated material from a thermostat region near 2 AU upward into the outer disk, enhancing bulk oxygen in the inner few AU. The association of this epoch with the first planetesimals remains tentative. Because HOPS-68 is less evolved than HOPS-315, the authors suggest that oxygen enhancement may persist over a prolonged phase of protostellar evolution.

PublicAstronomers studying the young star HOPS-68 find evidence that vaporized rocky material is cooling and forming crystals again in its surrounding disk. JWST detected several gases, including silicon monoxide, absorbing light above the disk’s hotter central plane. Modeling indicates gas temperatures of 300–500 kelvin and motion toward us relative to the star. ALMA observations also reveal a silicon-monoxide-rich jet and wind. Together with an earlier detection of silicate crystals, these observations lead the researchers to interpret the gas as material lifted by a disk wind from a hot region where solids vaporize. They conclude that HOPS-68 is experiencing a stage analogous to the earliest stage recorded in Solar System meteorites; whether this stage marks the formation of the first planet-building bodies remains uncertain. The inferred enrichment of oxygen in the inner disk, also found in the more evolved HOPS-315 system, may last through an extended period of young-star development.

Young explorerA baby star called HOPS-68 has a disk of gas and dust around it. Telescopes found warm gas moving above the hotter part of the disk, and scientists had already found tiny crystals there. The scientists think some rocky stuff gets so hot that it turns into gas, then a wind lifts it away so it can cool and become crystals again. This may be like something that happened very early when our own Solar System was forming. Scientists are not sure whether this is also when the first little building blocks of planets begin to form.

Small-Scale Magnetic Fields of Hyades M Dwarfs: Evolution with Age from the Pleiades to Field Stars

Fábio Wanderley, Katia Cunha, Oleg Kochukhov+9 more

AstronomerAnalysis of Zeeman broadening in magnetically sensitive APOGEE spectral lines yields mean small-scale magnetic fields of 0.7–4.3 kG for 18 Hyades M dwarfs. Comparison with previously studied Pleiades stars and exoplanet-hosting field stars gives sample means of 2965±632 G, 1925±1028 G, and 573±272 G for the Pleiades, Hyades, and field samples, respectively. The authors interpret these distinct distributions as reflecting age differences: the Pleiades sample is predominantly magnetically saturated, the roughly 500 Myr older Hyades sample spans saturated and unsaturated regimes, and the field sample is consistently unsaturated. A field-strength–Rossby-number relation derived from all three samples gives saturation limits of Ro_SAT=0.145 and mean field strength 2452 G. Cooler Hyades members tend to have stronger fields at a common age; this trend is less apparent in the other samples, attributed to the field stars’ broader age distribution and Pleiades saturation. Isochrone comparisons indicate positive correlations of field strength with radius inflation and photospheric spot coverage. Stronger fields also correlate with greater Hα equivalent-width excess and higher X-ray-to-bolometric luminosity ratios. These are observational correlations, not demonstrations of causation.

PublicResearchers used the magnetic broadening of spectral lines to estimate magnetic fields on 18 small, cool stars in the Hyades star cluster. Their average surface field strengths range from 0.7 to 4.3 kilogauss. Compared with earlier studies, the younger Pleiades cluster has stronger fields on average, while a sample of stars outside these clusters that host exoplanets has much weaker fields. The authors interpret the differences as reflecting stellar age. Many Pleiades stars lie in a magnetic saturation regime, where field strength levels off in the relationship studied; the Hyades stars span both saturated and unsaturated regimes. Among the Hyades stars, cooler stars tend to have stronger fields. Comparisons with stellar models also link stronger fields to greater enlargement of stellar radii and more surface spots. Stronger fields are associated with stronger signs of activity in stellar atmospheres and relatively brighter X-ray emission. These links do not by themselves establish that magnetic fields cause the other properties.

Young explorerStars can be like giant magnets. Scientists studied the light from 18 small stars in a group called the Hyades to work out how strong their magnetism is. These stars have weaker magnetism on average than stars in a younger group. The scientists think age helps explain the difference. In the Hyades group, cooler stars tend to be stronger magnets. Stars with stronger magnetism also tend to have more spots and more signs of activity in the gas around them. Those things go together, but this study does not prove that one makes the others happen.

Up in smoke: carbon-destruction in the terrestrial planet-forming region of a young Class I disk

F.J. Ballieux, M.K. McClure, E.A. Bergin+4 more

• Earth and Planetary Astrophysics

AstronomerAn LTE slab-model analysis of the JWST spectrum of the Class I protostar HOPS-68 detects warm (~400 K) HCN and C2H2 attributed to the base of a disk wind, and colder (~40 K) C4H2, CH3, and CS attributed to the outer disk or outflow cavity wall. The spectrum also contains 13CCH2, CH4, and C6H2; ALMA observations show C2H tracing the outflow cavity walls. The authors propose that thermal destruction of refractory carbon grains in the inner disk releases carbon-bearing species, which a disk wind transports outward as HCN and C2H2. UV-driven gas-phase reactions involving C2H could then form the observed aliphatic chains. This interpretation suggests that Warm Carbon Chain Chemistry might trace outflow rather than infall. Links to Earth's carbon depletion and to aliphatic organics in meteorites and asteroids remain proposed implications, not demonstrated outcomes.

PublicEarth's surface and deep mantle contain much less carbon than the Sun, and heating of carbon-rich dust near a young star is one possible explanation. Studying the young star HOPS-68, researchers used JWST spectra and models to identify carbon-bearing molecules in warm gas near the base of a wind from its disk and in much colder gas farther out. ALMA observations also revealed a carbon-bearing molecule along the walls of the outflow cavity. The researchers propose that heat releases carbon from inner-disk dust and that the wind carries some of it outward, where ultraviolet-driven reactions could build carbon chains. If correct, this would mean that a type of carbon-chain chemistry sometimes associated with falling-in gas might instead mark outgoing gas. Possible connections to Earth's carbon shortage and the organic material in meteorites and asteroids are not yet established.

Young explorerAround a young star called HOPS-68, scientists found tiny bits of gas made with carbon. Some are warm and close to where a wind starts, and others are much colder and farther away. The scientists think heat might free carbon from dust near the star. A wind could then carry it outward, where light could help make little chains of carbon. They have found the gases, but they have not proved that this whole story happened. It might help explain why Earth has relatively little carbon and how some space rocks got carbon-rich materials.

On the Detectability of Compact Multi-Planet Systems via Gravitational Microlensing

Stephen R. Kane

• Astrophysics of Galaxies
• Instrumentation and Methods for Astrophysics

AstronomerThe authors calculate, rather than observe, the microlensing signature of TRAPPIST-1’s seven planets for a hypothetical 0.09-solar-mass lens at 4 kpc toward the Galactic bulge. The Einstein radius is approximately 1.21 AU, placing the planets at normalized separations of 0.010–0.051, well inside the lensing zone. After fitting a single-lens model that absorbs the barycentric dipole, first-order cancellation of the quadrupole between the two images leaves an octupole-order residual scaling as q s^3, with fractional magnification deviations around 10^-6. All seven planets together produce Δχ² around 10^-3 even at 1 mmag precision, five orders of magnitude below the standard detection threshold. Detectability requires multiplying all planet masses by roughly 300, whereas guaranteed Hill stability of the resonant chain is lost at a factor of roughly 7; this does not establish instability. Only a lens within roughly 15 pc of the source or the Sun puts the outer planets in the lensing zone. The authors therefore predict that Roman will not detect TRAPPIST-1-like systems through microlensing, while its transit observations in the same fields could detect many such planets.

PublicCould seven tightly packed planets reveal themselves together by changing how their star bends light from a background star? Calculations using TRAPPIST-1 as a model suggest not for a typical distant lens. Even the combined signal of all seven planets falls far below the usual detection threshold in the setup studied. This is a theoretical calculation, not an observed failure to detect planets. A lens very close to either the Sun or the background star would provide more favorable geometry. The authors predict that the Nancy Grace Roman Space Telescope will not find TRAPPIST-1-like systems through this light-bending method, but could find many through transits—the small dips in starlight when planets cross in front of their star.

Young explorerA star can bend light from a star behind it, and planets can change that light a little. Scientists worked out what seven planets like those around TRAPPIST-1 would do. In their pretend faraway setup, even all seven made a change too tiny to spot. They expect the Roman space telescope could instead find many such planets by watching them pass in front of their own stars and block a little light.

Constraining Ganymede's Interior Structure and Bulk Composition from Its Present-Day Magnetic Field Strength

Jun Kimura, Ryohei Kawakami, Taro Matsuo+1 more

AstronomerGanymede’s small moment-of-inertia factor supports a differentiated interior, but its bulk composition and layer thicknesses remain uncertain. This study couples long-term thermochemical evolution with dynamo generation, using the observed equatorial surface field of approximately 719 nT to filter interior models initially consistent with chondritic compositions and geodetic constraints. Simulations permit dynamos in fully molten, Fe-snow, and FeS-layer regimes, but matching the observed field preferentially requires a relatively large core and a specific non-eutectic bulk core sulfur concentration. The models identify hydrosphere density as an independent constraint on compositional degeneracy: L- and CI-chondrite parameter spaces can sustain comparable fields for a hydrosphere density of 1,200 kg m-3, while H-chondrite models can do so at 1,300 kg m-3. These are model-dependent predictions, not determinations of Ganymede’s composition, and provide tests for JUICE, expected to arrive in 2031.

PublicGanymede is the only moon in our Solar System with a global magnetic field generated by its core. Its interior appears to contain a metallic core, a rocky mantle, and an outer water-rich layer, but their sizes and exact makeup remain uncertain. Researchers simulated how different possible interiors would cool, change chemically, and generate magnetism over time. Requiring the simulations to reproduce the measured magnetic field narrowed the possibilities, favoring a relatively large core with a particular sulfur content. The models also suggest that measuring the density of the outer water-rich layer could help distinguish between possible starting materials: different meteorite-like compositions match the field under different assumed densities. These predictions do not yet establish what Ganymede is made of; they offer a framework for testing with the JUICE mission, expected to arrive in 2031.

Young explorerGanymede is a moon with a magnetic field made deep inside it. Scientists do not know exactly what all its hidden layers are like. They used computer models to try different insides and see which could make a magnetic field like the one we measure. The models favored a fairly big metal center with a particular amount of sulfur mixed in. They also suggest that learning how much material is packed into its outer watery layer could help us choose between the possibilities. These are ideas to test, not a peek inside the moon. A mission called JUICE may help check them.

The impact of M dwarf stellar convection on exoplanetary atmospheric signatures. A 3D radiation-hydrodynamics simulation analysis for high-resolution spectroscopy

A. Chiavassa, M. Brogi, T. Masseron+3 more

• Solar and Stellar Astrophysics

AstronomerThis study combines 3D radiative hydrodynamical simulations of M-dwarf convection, synthetic spectroscopy, and transit modeling to investigate stellar contamination in high-resolution exoplanet spectra. Comparison with observations of GJ 3470 finds only modest agreement in water-line strengths and positions within the selected K-band interval, indicating remaining inaccuracies in current H2O line lists. In the modeled transit sequence of Neptune-size GJ 3470 b, centre-to-limb variations and the Rossiter-McLaughlin effect produce signals comparable in amplitude to planetary signatures. PCA can in principle remove these stellar effects, but its performance depends strongly on the simultaneous presence of telluric and planetary signals. The analysis recovers the planetary signal without evident bias from stellar residuals, but this finding is restricted to a narrow spectral interval and one orbital configuration. The framework supports future efforts toward unbiased ELT measurements; it does not establish general immunity to stellar contamination.

PublicSmall, temperate planets around M-dwarf stars are attractive targets, but motion in the stars' surfaces can complicate the light measurements used to study them. Researchers simulated this surface motion and compared the resulting spectra with observations of the star GJ 3470. They found that reference data for water's spectral lines still reproduce the observations only modestly in the wavelength range studied. They also modeled a transit of the Neptune-size planet GJ 3470 b, finding that changes in the star's light during the crossing can be as strong as the planet's signal. A statistical cleanup method recovered the planetary signal without an obvious bias from leftover stellar effects in this analysis. However, its performance depended on signals from Earth's atmosphere and the planet, and the test covered only a narrow wavelength range and one orbital arrangement. The work provides a basis for improving future Extremely Large Telescope observations, rather than proving that stellar interference can always be removed.

Young explorerWhen a planet passes in front of a star, scientists study the light to learn about the planet. But the star's own moving surface can change the light too, making the planet's clues hard to pick out. Scientists made computer models of a star and a planet crossing it, and checked some of their pretend starlight against real observations. Some water clues in the model did not match very well. A cleanup method helped them find the planet's signal in their test, with no obvious mix-up from leftover star clues. But they tested only a small part of the light and one kind of crossing, so they do not yet know how well it will work in other cases.

Orbital Architecture of Super-Earth-Cold-Jupiter Systems from Transit Duration Ratios

Tom Lassmann, Joseph Hand, Fei Dai+3 more

AstronomerThe study compares super-Earth systems hosting cold Jupiters with other Kepler-like systems using normalized transit durations T/T0 and neighboring-planet duration ratios ξ. It finds no population-level difference in T/T0. Forward modeling of ξ finds no evidence for larger mutual inclinations in the cold-Jupiter sample, with hints that these systems may be flatter. The inferred Rayleigh mutual-inclination dispersion is approximately 1.0°, versus 1.5° in the comparison sample; assuming equipartition, the corresponding characteristic eccentricities are approximately 0.035 and 0.05. The dynamical analysis indicates that secular coupling among the inner super-Earths usually dominates forcing by the distant giant, helping preserve nearly coplanar, low-eccentricity architectures. These conclusions apply only to systems with multiple transiting super-Earths: strongly excited systems are expected to appear as single-transiting and cannot be assessed with ξ. Undetected cold Jupiters in the comparison sample could also dilute the measured ξ distribution.

PublicDo distant giant planets disturb the orbits of smaller planets closer to their star? This study compares systems containing super-Earths and a cold Jupiter with other similar planetary systems. Overall, the researchers find no difference in one measure of how long planets take to cross their stars. Modeling the relative crossing times of neighboring planets finds no evidence that the systems with distant giants have more tilted inner orbits, and hints that they may be even more closely aligned. The analysis suggests that gravitational interactions among the inner planets often help them resist disturbance by the giant. But the study only covers systems where multiple inner planets cross the star from our viewpoint. More strongly disturbed systems may show only one crossing planet and therefore be excluded. Unrecognized giant planets in the comparison group could also blur differences.

Young explorerA big planet far from a star might tug smaller planets onto tilted paths. The researchers studied systems where several small planets pass in front of their star. They found no sign that having a faraway giant makes those small planets’ paths more tilted. Their calculations suggest the small planets can help keep one another lined up. But there is a catch: if their paths are very tilted, we might see only one planet cross the star, so this test would miss them. Some systems in the other group might also have giant planets that have not been found.

Orientation of the spin axes of large Kuiper belt bodies as an indicator of the mechanism of their origin

A. M. Kazantsev

AstronomerThe study examines spin-axis orientations of Kuiper Belt bodies with satellites, estimating most orientations by assuming that satellite orbital planes are close to the primaries’ equatorial planes. Large scattered-disk bodies and plutinos, including four dwarf planets, are found to have spin axes at relatively small angles to their heliocentric orbital planes. The authors interpret this pattern as suggesting the possibility that all scattered-disk bodies and objects in Neptune’s 3:2 resonance originated in the disruption of one large body, rather than establishing that origin. Spin-axis orientations of cold-component Kuiper Belt bodies may provide further evidence for their proposed distinct origin.

PublicThe paper studies how Kuiper Belt objects with moons are tilted as they spin. For most objects, the researchers inferred the spin direction by assuming that the moons orbit close to the parent object’s equator. They found that the spin axes of large scattered-disk objects and plutinos, including four dwarf planets, lie relatively close to the planes of their paths around the Sun. This pattern suggests, but does not prove, that all scattered-disk objects and plutinos could be fragments of one large body. The spin directions of another group, the Kuiper Belt’s cold component, may offer further clues that it formed differently.

Young explorerFar beyond Neptune, icy worlds spin like tops, and some have moons. Scientists used those moons to help guess which way the worlds spin, assuming the moons circle near each world’s middle. They found that some worlds’ spinning axes lie almost flat against the planes of their paths around the Sun. That could be a clue that a whole group came from one big world that broke apart, but it is not proof. The way other icy worlds spin might help show that they had a different beginning.

Migration and eccentricity damping timescales in overstable resonant planetary systems: hydrodynamic and N-body simulations

Zahra Afkanpour, Sareh Ataiee, Anna B. T. Penzlin+5 more

AstronomerHydrodynamic simulations of two-planet systems undergoing resonant and overstable evolution near the 2:1 mean-motion resonance test the constant migration and eccentricity-damping timescales commonly used in analytical and N-body models. Across varying disc surface densities, viscosities, and aspect ratios, timescales inferred from planet–disc energy and angular momentum exchange vary with time and exhibit sign reversals in resonant systems owing to eccentricity oscillations and disc torque variations. Normalising migration timescales by their expected mass, surface-density, and aspect-ratio dependence does not remove differences between models, and the usual migration–damping timescale relation is not recovered. Constant-timescale N-body prescriptions fail to reproduce the hydrodynamic evolution. Torque-based prescriptions incorporating corotation torque saturation and planetary eccentricity reproduce the type I migration evolution, but require additional corrections for planets that partially open gaps. These simulation results support time-dependent torque prescriptions for simplified models of resonant planetary systems.

PublicA disc of material surrounding planets can change both the sizes and shapes of their orbits. Simplified calculations often assume that these changes happen on fixed timescales. This study tests that assumption using computer simulations of two planets near a configuration in which one circles their star about twice for every orbit of the other. In the simulations, the timescales change as the planets and disc interact, and the direction of the orbital changes can sometimes reverse. Simplified models using fixed timescales do not reproduce the simulated evolution. Models that instead track the disc’s changing twisting forces agree better, especially when they account for the planets’ orbital shapes and how part of the disc’s force weakens. Those models still need corrections when planets partly clear gaps in the disc. The findings come from simulations, not observations of planetary systems.

Young explorerScientists used computers to imagine two planets going around a star inside a disc of material. The material can push and pull on the planets, changing their paths. The computer experiments showed that these changes do not always happen at a steady pace, and can sometimes switch direction. Simple planet models worked better when they allowed the pushes and pulls to change. But they still need fixing when planets start making gaps in the material. This was a computer experiment, not something scientists watched happen in the sky.

Preparing for the Gaia DR4 Epochalypse: Simulated Epoch Astrometry for Substellar Companion Orbit-Modeling Benchmarks

Daniel A. Yahalomi, Adrian M. Price-Whelan, Jessica Speedie+13 more

• Instrumentation and Methods for Astrophysics

AstronomerThe epochalypse catalog provides simulated Gaia DR4-like epoch astrometry for benchmarking orbit-modeling pipelines against known injected parameters. Each of 5,040,328 main-sequence G23H stars within 500 pc receives zero-, one-, and two-companion realizations, yielding 15,120,984 systems and a matched companion-free null sample. Companion masses and semimajor axes are sampled log-uniformly over 1 Mars mass–80 Jupiter masses and 0.03–100 au, without an occurrence model or detectability cut. Potentially detectable subsets are flagged using estimated signal-to-noise ratios accounting for stellar noise, transit counts, and long-period signal suppression. A kepmodel astrometric-periodogram demonstration on the simulations shows that detection and period localization decouple beyond the DR4 baseline: significant curvature need not yield well-constrained periods or masses. The authors argue that, under any companion occurrence model, detectable but uncharacterizable systems will far outnumber those with fully characterizable orbits. These are simulation-based findings, not new companion detections. The catalog, generation pipeline, and tutorial are publicly available.

PublicGaia's forthcoming fourth data release could reveal tens of thousands of companions through the small changes they cause in stars' positions. To prepare, researchers created more than 15 million simulated systems with zero, one, or two companions, using real catalog stars as starting points. The simulations span a wide range of companion masses and orbits; they are a testing resource, not a prediction of how common those companions actually are. A demonstration reveals an important limitation: a companion with an orbit longer than the observing span may noticeably bend a star's apparent path while leaving the companion's orbital period and mass poorly determined. The researchers argue that such detectable but poorly characterized systems will greatly outnumber systems whose orbits can be fully characterized. The simulated catalog and tools are publicly available to help researchers prepare their analysis methods.

Young explorerA space telescope called Gaia watches where stars are. A nearby companion can make a star wobble. Scientists made millions of pretend star systems to practice finding those wobbles before Gaia's next big set of information arrives. In their practice test, they found that seeing a wobble does not always tell you how long the companion takes to go around or how heavy it is, especially when its trip takes longer than Gaia has watched. These are pretend systems for testing, not newly discovered companions.

A Smooth Transition from Giant Planets to Brown Dwarfs from the Radial Occurrence Distribution

Judah Van Zandt, Greg Gilbert, Steven Giacalone+3 more

• Solar and Stellar Astrophysics

AstronomerCombining legacy radial velocities with absolute astrometry, the authors refit 194 California Legacy Survey companions to constrain true masses rather than RV minimum masses, M_c sin i. Seven of 18 nominal brown dwarfs with minimum masses of 13–80 Jupiter masses instead had true masses above 80 Jupiter masses. Orbital posteriors and target sensitivity maps were incorporated into a Poisson likelihood model to infer occurrence over 0.8–80 Jupiter masses and 0.3–30 AU. The inferred semimajor-axis distributions vary smoothly with mass: Jupiter analogs favor an abrupt occurrence increase near 1 AU, whereas brown dwarfs show a gradual enhancement at wider separations. Integrated over 1–10 AU, occurrence decreases smoothly with mass, reaching 1.1% (+0.5, −0.4 percentage points) for brown dwarfs. Jupiter analogs are about ten times as common per mass interval, extending the inferred brown dwarf desert to 10 AU. The smooth mass dependence disfavors, but does not rule out, a sharp transition between core accretion and gravitational instability; the authors interpret it as suggesting overlapping companion-mass ranges for these formation processes.

PublicA companion’s pull makes its star move, but measurements of motion toward and away from us reveal only the companion’s minimum mass. This can make a heavier object look like a giant planet or brown dwarf. By combining those measurements with precise measurements of stellar positions, researchers reassessed 194 companions. Seven of 18 objects initially classed as brown dwarfs by minimum mass actually exceeded 80 Jupiter masses. After accounting for detection sensitivity, the team estimated that brown dwarfs occur around 1.1% of surveyed stars at separations of 1–10 astronomical units, with an uncertainty of roughly half a percentage point. Jupiter-like planets were about ten times more common per mass interval there. How companions are distributed in distance changes smoothly with mass. The authors interpret this as evidence against a sharp mass boundary between two proposed formation processes, suggesting instead that those processes may produce companions with overlapping masses.

Young explorerSomething going around a star can make the star wiggle. But one kind of wiggle measurement can make that hidden companion seem lighter than it really is. Scientists combined two kinds of measurements and found that some companions were heavier than they first seemed. They also estimated that Jupiter-like planets are much more common than objects called brown dwarfs. Their findings suggest that two different ways of making companions might make some of the same sizes, but that is not certain.

Effect of tidal gravity and planetary rotation on the retrieved atmospheric abundances of close-in exoplanets

K. Arnav, Gopal Hazra

• Solar and Stellar Astrophysics

AstronomerThis study incorporates rotational and stellar tidal corrections to effective gravity into atmospheric forward and retrieval models for tidally locked, close-in exoplanets. Applied to HST observations of WASP-12b and JWST observations of WASP-121b, retrievals with and without these corrections yield different inferred molecular abundances. Forward calculations predict transit-depth increases of 300–600 ppm for major molecules in WASP-12b, where gravity is more strongly reduced, and variations of 60–140 ppm in WASP-121b. These are modeled changes, not directly measured gravity-induced signals. Synthetic injection-recovery tests across a broad wavelength range show statistically significant parameter shifts for simple atmospheric compositions, but smaller shifts for more complex compositions because of increased retrieval degeneracies. Tests with non-isothermal pressure–temperature profiles and cloudy models preserve the qualitative trends.

PublicA planet’s spin and the gravity of its nearby star can change the effective gravity in its atmosphere, affecting how spread out the gas is and how scientists infer its chemical makeup. The researchers built these effects into models and used them to analyze Hubble observations of WASP-12b and James Webb observations of WASP-121b. Including the corrections changed the inferred amounts of atmospheric molecules. Their calculations also predicted changes in how much starlight the atmospheres block during a transit, with larger effects for WASP-12b. Those predicted changes are not direct measurements of the effects. Tests using simulated observations found statistically significant shifts in inferred atmospheric properties for simple gas mixtures, but smaller shifts for complex mixtures, where different explanations can fit the data. Models allowing temperature to vary with pressure and including clouds retained the same general trends.

Young explorerWhen a planet passes in front of its star, some starlight travels through the planet’s blanket of gas. Scientists use that light to work out which gases are there. This study used computer models that include the planet’s spinning and the star’s pull, which can change how spread out the gas blanket is. Using these models with telescope observations of two planets changed the scientists’ estimates of how much of each gas was there. Tests with pretend observations showed clearer changes for simple gas mixtures and smaller changes for complicated mixtures, which are harder to figure out. These are clues from models, not proof that telescopes directly saw the changes caused by spinning and the star’s pull.

Gemini and Apache Point Multi-band Optical Imaging Characterization of Fragmenting Long-period Comet C/2025 K1 (ATLAS)

Carl Ingebretsen, Bryce T. Bolin, Meredith A. MacGregor+8 more

AstronomerMulti-band imaging of C/2025 K1 (ATLAS) with Gemini North/GMOS on 2025 December 6 and 24 and ARC/ARCTIC on December 8 identifies at least four distinct fragments, designated A, C, D, and E. Color indices were measured for A and C on December 8 and for A, C, and D on December 24. The comet has an unusually blue g-r color of approximately 0.40. Particle-size and light-scattering effects are offered as a possible explanation for the reported color differences between the comet and its fragments at the two epochs. Dust mass-loss rates were calculated from the Gemini observations for A, C, and D; for millimeter-sized dust, the authors infer moderate rates of approximately 50 kg/s for fragments A and C.

PublicImages taken with the Gemini North and ARC telescopes in December 2025 reveal at least four separate fragments of comet C/2025 K1 (ATLAS). Observations through several color filters show that the comet has an unusually blue color. Differences in dust-particle sizes and the way the particles scatter light may explain the reported color differences between the comet and its fragments, but this explanation is not established. From the Gemini images, the researchers estimate that fragments A and C each shed millimeter-sized dust at about 50 kilograms per second, which they describe as a moderate rate.

Young explorerAstronomers took pictures of a comet and saw at least four separate pieces. They also found that the comet looked unusually blue when they compared its light through different color filters. Tiny bits of dust might help explain why the comet and its pieces have different colors, but the scientists are not sure. They used the pictures to estimate that two of the pieces were each losing about 50 kilograms of dust every second.

Composition gradients in sub-Neptunes: K2-18 b and TOI-270 d as case studies

Luca Morf, Ravit Helled

AstronomerThis modeling study compares distinct, compositionally homogeneous, purely adiabatic layers with interiors containing composition gradients and stable non-convective regions for K2-18 b and TOI-270 d. Both approaches yield solutions consistent with the observed masses, radii, and atmospheric boundary conditions, but composition gradients substantially broaden the allowed structures and bulk compositions, even at fixed mass and radius. Relative to the purely adiabatic models, the maximum permitted H-He mass fraction for K2-18 b increases by about threefold at a 1 bar temperature of 300 K and tenfold at 600 K; for TOI-270 d, it generally increases by more than an order of magnitude. For both planets, the Spearman correlation between H-He and iron abundances falls from approximately 0.7 to 0.3, with similar weakening for H-He abundance versus rock-to-iron mass ratio. Other correlations, including H-He abundance versus water-to-rock mass ratio, persist or strengthen. These are model-dependent allowances, not measurements of the planets' interior compositions. The authors conclude that purely adiabatic models understate compositional degeneracy and overstate how much improved observations and external constraints can resolve it, and recommend including more complex interiors by default.

PublicThe measured masses and sizes of K2-18 b and TOI-270 d do not uniquely reveal what is inside them. This study compares models with sharply separated, uniform layers against models in which composition changes gradually and some regions do not mix by convection. The more complex models allow a much wider variety of interiors while still matching the available observations and atmospheric conditions. In particular, the largest allowed hydrogen-helium content can be several times higher for K2-18 b, depending on the assumed atmospheric temperature, and generally more than ten times higher for TOI-270 d. This does not show that either planet actually contains that much gas or has a gradual change in composition. It shows that simpler models can make scientists too confident about what the planets contain and how much better measurements will narrow the possibilities. The authors recommend routinely considering more complex interiors when interpreting these planets.

Young explorerScientists know how heavy and how big two faraway planets are, but they cannot tell exactly what is inside. They tried different ways of imagining the planets' insides. Some had neat, separate layers; others had materials that changed little by little, with some parts that did not stir. The less tidy versions gave many more possible answers that still fit what scientists have measured. That does not mean the planets really look that way inside. It means scientists should check more possibilities before deciding what these planets are made of.

TOI-6981 b: a transiting sub-Neptune at the water ice line

Madison G. Scott, Amaury H.M.J Triaud, Emily K. Pass+42 more

AstronomerThe SPECULOOS TEMPOS program presents TOI-6981 b, a validated sub-Neptune with a radius of 2.51 ± 0.11 Earth radii and a 60.8-day orbit around an M4 star. Its planetary nature is supported by ground-based follow-up photometry, statistical validation, and high-resolution spectroscopy. Assuming an Earth-like albedo, its equilibrium temperature is 175 K (+6/−5 K), placing it near the approximate 170 K water ice line in temperature. Its transmission spectroscopy metric of 56 ± 10 makes it a promising target in the sparsely populated cold-planet regime for JWST atmospheric studies. Such observations could test cold atmospheric chemistry and Hycean-world hypotheses and enable comparisons with the Solar System’s ice giants; these are prospective applications, not reported atmospheric findings. Its current orbit may also inform studies of formation and migration at or beyond the water ice line.

PublicAstronomers have validated TOI-6981 b, a planet about 2.5 times Earth’s radius that circles a small M4-type star every 60.8 days. Assuming it reflects light like Earth, its estimated equilibrium temperature is about 175 kelvin, near the roughly 170-kelvin temperature associated with the water ice line. That estimate does not establish that the planet contains ice or oceans. The planet is a promising candidate for studying a cold atmosphere with JWST, although the abstract reports no atmospheric observations. Future studies could explore its chemistry, test ideas about ocean-bearing worlds with hydrogen-rich atmospheres, and investigate how planets form and move near or beyond the water ice line.

Young explorerAstronomers found a planet called TOI-6981 b going around a small star. It is about two and a half times as wide as Earth and takes about 61 days to go around its star once. They estimate that it is very cold, but they have not shown that it has ice or an ocean. They hope to use the JWST telescope to learn about the air it might have and how planets like it came to be.

Experimental evidence for a physical alteration of fine regolith on near-Sun asteroids

Jooyeon Geem, Mikael Granvik, Georgios Tsirvoulis+5 more

• Instrumentation and Methods for Astrophysics

AstronomerLaboratory experiments exposed CM-type carbonaceous chondrite simulants under vacuum to irradiation representing near-Sun conditions at 0.09–0.19 au. In situ video monitoring and post-heating microscopy showed initial darkening followed by brightening, consolidation, and morphological changes spanning sub-micrometer to millimeter scales. The brightness changes are more consistent with altered absorption properties than with surface-roughness variations. SEM images revealed sintering-like structures absent from unheated samples, suggesting sintering as a likely mechanism for the consolidation and morphological changes. These laboratory results help constrain near-Sun asteroid surface evolution and support, but do not establish, the proposed sintering mechanism for (3200) Phaethon.

PublicResearchers tested how intense sunlight might change the surfaces of asteroids that pass close to the Sun. In a vacuum, they heated material made to resemble a type of carbon-rich meteorite, recreating irradiation conditions at distances of 0.09–0.19 times Earth's distance from the Sun. The samples first darkened, then brightened, became more consolidated, and developed changes visible under microscopes. The brightness changes appear more consistent with changes in light absorption than with changes in surface roughness. Some microscopic structures resembled those produced by sintering, in which heating bonds grains together. The experiment supports sintering as a possible process on near-Sun asteroids, including Phaethon, but does not show that it actually occurs there.

Young explorerScientists wanted to know what strong sunshine might do to an asteroid's surface. They used special pretend space rocks and heated them in a laboratory to copy conditions close to the Sun. The material got darker first, then brighter, and became more stuck together. Looking through microscopes, they saw shapes that suggest heat may have helped tiny grains join together. That might happen on some real asteroids too, but this test does not prove it.

Missing Outer Rings in the exoALMA Sample: Physical Mechanisms Suppressing Dust Ring Formation Despite Strong Pressure Bumps

Lilian Luo, Paola Pinilla, Jochen Stadler

AstronomerFor nine exoALMA discs, the study reconstructs gas surface density profiles from midplane pressure gradients inferred from 12CO and 13CO ALMA Band 7 observations, then models dust evolution with DustPy and continuum emission with RADMC-3D. Across the tested turbulence and fragmentation parameters, efficient dust trapping at candidate pressure bumps beyond the observed millimetre continuum discs generally predicts prominent outer rings detectable in Band 7, in tension with observations. The 13CO-based reconstructions almost universally predict detectable rings; the 12CO-based results are more varied. Of the suppression mechanisms tested, enhanced outer-disc turbulence weakens predicted emission most effectively, but its efficacy depends on the system and the turbulence transition location. Delayed bump formation generally fails to prevent rapid outer dust accumulation. These are model predictions, not detections of outer dust rings.

PublicObservations of several young planet-forming discs suggest possible gas-pressure bumps beyond the regions where millimetre dust emission is seen. Could these outer regions contain hidden dust structures? Researchers studied nine discs, using gas observations to build models of how dust would move and how brightly it would shine. Most models predict that the pressure bumps would collect dust into outer rings bright enough for ALMA to detect, which conflicts with the observations. Predictions differ depending on which gas tracer is used to reconstruct the disc. Stronger turbulent motion in the outer disc reduces the predicted ring brightness most effectively among the options tested, although its success varies with the disc and where the stronger turbulence begins. Making the pressure bump form later generally does not stop dust from gathering quickly.

Young explorerAround young stars, gas and dust make big, flat discs. Scientists found clues that some discs might have gas bumps outside the dust they can see. They used computer models to ask whether those bumps could gather dust into rings. Usually, the models made rings bright enough to see, but the observations do not show those bright rings. Making the gas more swirly helped make the pretend rings fainter, though it worked better in some discs than others. Making the bump appear later usually did not stop the dust from piling up.

Online learning of subgrid-scale models for quasi-geostrophic turbulence in planetary interiors

Hugo Frezat, Thomas Gastine, Alexandre Fournier

• Fluid Dynamics
• Machine Learning

AstronomerThis simulation study extends online, end-to-end learning of subgrid-scale closures to two-dimensional quasi-geostrophic turbulence in rapidly rotating, mechanically bounded annular domains. Three configurations vary container geometry and rotation rate. The simulated flows exhibit zonal jets and Rossby waves, with slow, quasi-periodic inward jet migration in the spherical-shell geometry; their zonal and non-zonal spectra are interpreted within zonostrophic turbulence theory. A differentiable solver enables online training using coarse-grained direct numerical simulation data over one turnover time. In all three tested configurations, the trained closure accurately reproduces global integrated diagnostics, energy spectra, and long-term dynamics, including jet migration on timescales about ten times the training window. It outperforms classical hyperdiffusivity and Leith closures, for which reducing radial resolution is reported to be impractical. The resulting speed-up offers a route to studying longer-term geophysical fluid processes; the reported validation concerns these simulated configurations, not observations of planetary interiors.

PublicThe researchers tested whether machine learning can make simulations of rotating fluids more efficient without losing their slow, large-scale behavior. Such flows are relevant to planetary interiors, but earlier learning-based studies mostly lacked solid boundaries. Here, the team simulated three bounded, ring-shaped configurations with different shapes and rotation rates. They trained models to represent unresolved small-scale motion using detailed simulation data spanning one characteristic circulation time. In the tested cases, the models reproduced energy patterns and longer-term behavior, including slowly moving bands of flow, over timescales about ten times longer than the training period. They also performed better than two conventional modeling methods. These are simulation results, not planetary observations; the speed-up could enable future studies of fluid processes too costly to follow with fully detailed simulations.

Young explorerImagine making a computer picture of liquid swirling inside a spinning ring. Tiny swirls are hard for the computer to keep track of. The researchers taught it a shortcut using a short piece of a very detailed simulation. In their tests, the shortcut still copied big patterns much later, including slowly moving bands of flow. It could help computers study swirling liquids for longer.

Stable Ballistic Prograde Cyclers in the Three-Body Problem

Shane D. Ross, Michael Roberts-Tsoukkas

• Chaotic Dynamics
• Classical Physics

AstronomerThe authors report the first continuous families of stable, ballistic, prograde cyclers in the circular restricted three-body problem: periodic trajectories alternating between temporary capture around each primary. They construct symmetric families from intersections of the stable and unstable manifold tubes of the L1 Lyapunov orbit, finding stable examples across more than two orders of magnitude in mass ratio, from the Sun–Jupiter regime to equal masses. In every computed family, a saddle-center bifurcation at the maximal Jacobi constant creates planar-stable and hyperbolic branches; out-of-plane instability arises only through isolated parametric resonances. Each computed family contains a subfamily linearly stable to both planar and out-of-plane perturbations. Stable cyclers persist in the full three-body problem for sufficiently small third mass. These are dynamical-model findings, not observed orbits; universal saddle-center birth and the generic occurrence of stable cyclers remain conjectures.

PublicCalculations reveal continuous families of repeating paths that let a small body alternate between temporarily orbiting one of two larger bodies and then the other, without propulsion. The authors find stable examples in an idealized gravity model, covering mass ratios from a Sun–Jupiter-like pairing to two equal masses. Every family they computed includes paths stable against small disturbances both within and outside the orbital plane. The stable paths also persist in a model where the third body's mass is included, provided that mass is sufficiently small. This is a theoretical result, not a discovery of objects following these paths in space. The authors suggest that stable alternating orbits may be a common feature of three-body motion, but that broader claim remains unproven.

Young explorerImagine a tiny space traveler looping around one big object, then the other, and repeating the trip without using an engine. Researchers used a math model of gravity to find whole groups of paths like this. Some paths can handle tiny nudges without becoming unstable. They have not spotted real travelers doing this in space, and their idea that these paths might be common is still a guess.

From Early Concepts to Lunar Hypertelescopes Roadmap for Next-Generation Optical Astronomy on the Moon

M. Hadjara, T. Xu, S. Lagarde+8 more

AstronomerThis review traces six decades of lunar observatory concepts, examines why most remained unrealized, and proposes a roadmap toward lunar hypertelescopes. Motivations include the absence of an atmosphere, mechanical stability, access to the radio-quiet far side, and scope for very large apertures. Earlier projects were constrained by technology, shifting scientific priorities, and the cost of sustained lunar operations. Renewed exploration efforts and advances in robotics, autonomy, additive manufacturing, precision optics, and formation flying are presented as enabling developments. Diluted optical arrays spanning hundreds of meters to several kilometres could potentially deliver unprecedented angular resolution; these are proposed capabilities, not demonstrated observational results.

PublicThe Moon has long appealed to astronomers because it has no atmosphere, offers a very stable surface, and has a far side shielded from radio interference. This paper reviews past plans for lunar observatories and why most were never built, including technical limits, changing scientific priorities, and high operating costs. It argues that renewed lunar exploration and developing technologies could make ambitious observatories more feasible. In particular, proposed hypertelescopes would spread optical elements across hundreds of meters to several kilometres, potentially allowing astronomers to distinguish exceptionally fine detail. The paper offers a roadmap for such facilities, rather than reporting a working lunar telescope or new observations.

Young explorerScientists have long imagined putting telescopes on the Moon. It has no air to blur the view, and its ground is very steady. But building and running telescopes there has been hard and expensive, so most ideas were never built. This paper looks at those old plans and suggests steps toward a new kind of telescope with many parts spread far apart. Someday, it might show much finer details in space. It is still a plan, not a telescope that has already done this.

From Earth's Harshest Landscapes to Lunar Horizons: Engineering NEA Telescopes for Extreme Environments

M. Hadjara, A. Pomazan, H. Ji+12 more

• Earth and Planetary Astrophysics

AstronomerThis paper proposes AMAS (Atacama-Mongolia-Antarctica-Sahara), an international programme to test specialized near-Earth asteroid survey telescopes at extreme terrestrial sites as analogues for future lunar observatories. The motivation is the substantial detection gap for NEAs smaller than approximately 140 m and the limited visibility of Sun-ward approaches from Earth, which can shorten warning times. Lunar telescopes could expand accessible observing regions and improve sensitivity and early detection, but must contend with thermal cycling, dust, radiation, and autonomous operation. The paper presents the scientific rationale, engineering challenges, site-selection strategy, and roadmap toward an Earth-Moon planetary-defense network; it does not report completed technology validation or demonstrated detection gains.

PublicMost large near-Earth asteroids have been detected, but many smaller than about 140 metres remain difficult to find, even though they can cause regional devastation. Objects approaching from the Sun’s direction are especially hard to spot from Earth, and weather and the atmosphere also limit searches. This paper proposes AMAS, an international effort to test asteroid-search telescopes in extreme environments on Earth as preparation for possible observatories on the Moon. Lunar telescopes could help find some asteroids earlier, but would need to withstand temperature swings, dust, and radiation and operate autonomously. The paper lays out a testing strategy and a long-term plan, rather than reporting a working lunar observatory or proven improvements in asteroid detection.

Young explorerSome space rocks come near Earth, and ones coming from the Sun’s direction are very hard for telescopes here to see. A telescope on the Moon might help us spot them sooner. But the Moon has dust, radiation, and big temperature changes that could make a telescope’s job difficult. The scientists suggest first testing special telescopes in very tough places on Earth. This is a plan to get ready, not something they have already shown works on the Moon.

HLA-Net: A Physics-Guided Skeleton-Based Framework for Automatic Gravitational Arc Detection in Astronomical Images

Don S

• Astrophysics of Galaxies
• Machine Learning

AstronomerThe authors propose HLA-Net, an interpretable, multi-stage gravitational-arc detection framework that combines geometric morphology with physical lensing characteristics without requiring manually annotated training data. Evaluated on astronomical FITS images containing complex galaxy-cluster structures, its verification pipeline reduced 169 initial candidates extracted from ordered skeleton representations to 83 geometrically consistent candidates. Robust circle fitting also modelled 113 candidate arc structures; the abstract does not specify how this set overlaps the 83 retained candidates. The authors report suppression of false positives while preserving physically reasonable lens candidates, but do not report confirmed lenses or quantitative completeness and purity. The work concerns automated candidate selection, not a new dark-matter distribution or cluster-mass measurement.

PublicGravity can bend light into arcs, which astronomers can use to study dark matter and the mass of galaxy clusters. Finding these rare, often faint shapes automatically is difficult. The researchers propose HLA-Net, a computer method that checks both arc shapes and their consistency with gravitational lensing, without needing manually labelled training examples. In tests on astronomical images, it narrowed 169 starting candidates to 83 geometrically consistent ones. A circle-fitting step also modelled 113 candidate structures, though their overlap with the 83 is not explained. The authors report fewer false detections, but these are still candidates, not confirmed gravitational lenses.

Young explorerGravity can bend light into curved shapes in space. These shapes can be faint and hard to find. The researchers made a computer helper that looks for them and checks whether their shapes make sense. When tested on space pictures, it kept a smaller group of promising shapes. The researchers say it helps reject mistakes, but the shapes it picked still need checking.

The PAU Survey: Self-supervised image denoising for flux-preserving photometry

J. Chen, M. Eriksen, D. Navarro-Gironés+12 more

• Cosmology and Nongalactic Astrophysics
• Astrophysics of Galaxies

AstronomerUsing real PAUS observations and PAUS-like simulations, the authors evaluate Noise2Void (N2V) for quantitative photometry and find that standard N2V systematically underestimates galaxy fluxes, particularly for faint sources. They introduce a bounded-output layer to limit large negative outputs, followed by low-rank adaptation (LoRA) with two flux-aware loss terms targeting flux-scale preservation and repeated-exposure consistency. For PAUS galaxies with 22 <= i_AB < 23 in NB645, the bounded-output model shifts the flux-ratio distribution peak back close to the original PAUS scale. Flux-aware LoRA fine-tuning yields a repeated-exposure flux-difference width of sigma_68 = 0.529, corresponding to an effective 47% reduction in random flux scatter relative to the original PAUS uncertainty scale, while retaining a median flux ratio close to unity. These results support photometric validation rather than image-quality metrics alone; agreement with the original PAUS scale should not be confused with an independent determination of true fluxes.

PublicRemoving noise from faint galaxy images can make brightness measurements less reliable if the processing also removes some of the galaxies' light. Using real observations from the Physics of the Accelerating Universe Survey and simulated images resembling them, the researchers found that the standard Noise2Void denoising method systematically made galaxies appear too faint, especially the faintest ones. They modified the method to limit large negative outputs and trained it further to preserve brightness measurements and improve agreement between repeated observations. In a tested group of faint galaxies in one survey band, the modified method brought measurements close to the original survey's brightness scale. Further training reduced random brightness scatter by an effective 47% relative to the original survey uncertainty scale. The study shows why cleaner-looking images are not enough: denoising must also be checked for its effects on scientific measurements.

Young explorerPictures of faraway galaxies can look grainy, and a computer can help tidy them up. But the researchers found that one cleanup method also made galaxies look too dim. They tested real space pictures and pretend ones, then changed the method to help keep the galaxies' light. In the real pictures they checked, the new method kept brightness closer to the original measurements and made measurements from repeated pictures agree better. The lesson is that a prettier picture is not enough: we must check that the cleanup has not changed what we want to measure.

Fast and accurate false-alarm probabilities for linear detection statistics in Poisson noise

Maayane T. Soumagnac, Eran O. Ofek, Shachar Israeli+1 more

AstronomerThe authors derive a deterministic method for calculating false-alarm probabilities for arbitrary linear detection statistics under Poisson noise, motivated by low-count astronomical imaging. By expressing the detection statistic as a compound Poisson random variable, they enable efficient computation using FFT-based methods and Panjer recursion. The calculation is exact up to numerical discretization. They report speedups of several orders of magnitude over simulations and access to false-alarm probabilities that would be computationally inaccessible through simulation. This is a statistical-method result, not a report of an astronomical detection. Open-source Python and MATLAB implementations are provided.

PublicIn images containing very few photons, random fluctuations can look like real signals. Assessing how often such false alarms occur usually requires many simulated datasets. This work develops a direct numerical calculation for measurements formed by adding weighted event counts, assuming the random counts follow Poisson statistics. The authors report that it runs several orders of magnitude faster than simulations and can calculate false-alarm probabilities that simulations cannot practically reach. The method is exact apart from the numerical approximation involved in representing the calculation on a discrete grid. It is motivated by astronomical imaging but also applies to other detection problems involving Poisson-distributed events; it does not report a new astronomical discovery.

Young explorerWhen a picture has only a few tiny bits of light, chance can make a spot look like something is there. Scientists want to know how often chance could trick them. The researchers made a faster way for a computer to work that out, instead of making lots and lots of pretend pictures. It works when the random light counts follow a particular counting rule, and the computer's number steps can still make a small difference to the answer. It is a new way to check a possible signal, not a newly found star.

Polarimetry with the Giant Magellan Telescope: A Scientific Justification & Technical Requirements Document

G. Grant Williams, Ramya M Anche, B-G Anderson+27 more

AstronomerThe abstract makes the case for exploiting polarization alongside optical and near-infrared flux spectra to constrain source geometry and magnetic fields, including spatially unresolved structures. It emphasizes that crucial model discrimination often requires 0.1% precision in the degree of polarization, making polarimetry photon-starved. For spectropolarimetry, this entails collecting over one million photons per spectral bin and therefore requires large-aperture telescopes for typical targets of interest. The anticipated light-gathering power of future Giant Segmented Mirror Telescopes is presented as an opportunity for major advances, not as a demonstrated observational result.

PublicLight from space carries information not only in its brightness and color but also in its polarization, which describes how its electric field is oriented. Measuring polarization can reveal the shapes and magnetic fields of astronomical sources, even when their details cannot be resolved directly. The challenge is collecting enough light: distinguishing between scientific models often requires polarization precision of 0.1%, and measurements that also separate light by color need more than a million photons in each small wavelength interval. The abstract argues that future Giant Segmented Mirror Telescopes could provide the light-gathering power needed for major discoveries; it does not report new observations.

Young explorerLight from space has clues hidden in the way it wiggles, not just in its color. Those clues can help astronomers learn about the shapes of faraway things and their magnetic fields, even when they cannot see tiny details. But they need to catch lots and lots of light to read the clues carefully. The writers say future giant telescopes could help. They are describing what those telescopes might make possible, not a new discovery.

Pushing the frontiers of low-frequency radio astronomy: An ultra-deep sub-arcsecond LOFAR image of ELAIS-N1

J. M. G. H. J. de Jong, L. K. Morabito, R. J. van Weeren+11 more

AstronomerUsing 200 hours of LOFAR observations at 115–168 MHz, the authors image 2.5 × 2.5 deg² of ELAIS-N1 with long-baseline calibration and imaging. They achieve a central point-source sensitivity of 5.3 μJy/beam at 0.33″ × 0.39″ resolution and an area-weighted sensitivity of 7.4 μJy/beam at 0.36″ × 0.45″. They report these as the deepest radio images below 1.28 GHz to date. Combining the new data with previously released 6″ LOFAR images yields 62,916 unique radio sources. Alignment using 95 Gaia quasars gives offsets of ΔRA = −3 ± 27 mas and ΔDEC = 2 ± 17 mas, measured for those same alignment sources. Instrumental Stokes I leakage into linear polarisation reaches as low as 0.12%, demonstrating potential for deep sub-arcsecond polarisation studies rather than reporting such a survey. The work demonstrates the computational feasibility of combining many observations for wide-field, sub-arcsecond imaging and provides a foundation for deeper and wider surveys in the LOFAR2.0 and SKA era.

PublicAstronomers combined 200 hours of observations from the LOFAR radio telescope to make exceptionally sensitive, sharp radio images of a sky region called ELAIS-N1, covering 2.5 by 2.5 degrees. The team reports that these are the deepest radio images yet made at frequencies below 1.28 GHz, revealing very faint radio emission while retaining fine detail. Combining the new images with earlier, lower-resolution LOFAR images produced a catalogue of 62,916 distinct radio sources. The researchers also checked positional accuracy against 95 quasars with Gaia positions and demonstrated low levels of instrumental contamination in measurements of radio polarisation. That test shows promise for future detailed polarisation studies; it is not itself a completed polarisation survey. The work shows that processing large amounts of data into sharp images over a wide area is now computationally feasible, laying groundwork for larger and deeper surveys.

Young explorerAstronomers used a telescope called LOFAR to listen to radio signals from space for 200 hours. They put the observations together to make pictures of one patch of sky that show very faint things and tiny details. With help from older pictures, they made a list of 62,916 places where radio signals come from. They also checked how well the pictures show where things are. Their work shows they can make big, detailed radio pictures, and it could help them make even bigger and deeper pictures in the future.

Developing the Field Selector System for the SHARP Multi-IFU: Optomechanical Design and First Prototype Validation

H. Mahmoodzadeh, P. Saracco, I. Di Antonio+16 more

AstronomerThe paper presents a proposed Field Selector System for VESPER, the multi-integral-field unit of the SHARP near-infrared spectrograph. Movable light-collection probes occupy parallel, vertically offset planes to avoid mechanical interference and vignetting. For a probe displacement Δy, folding mirrors move by Δy/2, maintaining a constant optical path length so independently positioned probes can share a focal plane and form a continuous image for slicing. A dedicated optical test setup characterized probe positioning stability and repeatability; measured mechanical errors were converted to equivalent optical tilts and incorporated into the SHARP optical model to assess performance impacts. The experiments identified dominant positioning-error sources, although the abstract gives no numerical tolerances or performance metrics. The authors conclude that the concept is viable and identify design improvements expected to reduce probe tilt and improve stability; the claimed suitability for SHARP and other mIFU spectrographs is conditional on those improvements.

PublicThis study develops and tests a way to direct light from several selected targets into a near-infrared instrument. The proposed system uses movable light-collecting probes arranged on offset levels so they do not collide or block the light. As a probe moves, folding mirrors move half as far, keeping the light’s travel distance constant and allowing the probes to deliver their images to a shared focal plane. Laboratory tests measured how steadily and repeatably the probes moved. The researchers then used those measured errors in an optical model to assess their effects on instrument performance. The tests revealed the main sources of positioning error and supported the feasibility of the approach. Further design changes are expected to reduce probe tilting and improve stability, but the abstract does not report measured performance after those changes.

Young explorerThe researchers are working on a tool with little movable parts that pick up light from different places. The parts move on different levels so they do not bump into each other. Mirrors move too, but only half as far, to keep the light’s journey the same length. The team tested how well the parts moved and found what made them wobble or stop in the wrong place. The tests suggest the idea can work, and the team has ideas to make it steadier. Those improvements still need to be shown to work.

SHARP: A spectrograph proposal to fully exploit ELT capabilities

P. Saracco, P. Conconi, C. Arcidiacono+45 more

AstronomerSHARP is a concept study for a 0.95–2.45 μm near-infrared spectrograph designed to exploit the collecting area and angular resolution of ESO’s upcoming ELT. Its science drivers span astrophysics and cosmology in the local and distant Universe, motivating two complementary units: NEXUS, a multi-object spectrograph optimized for the faintest sources, and VESPER, a multi-object integral-field unit intended for brighter sources. The presentation outlines the science requirements, design solutions, and an optical design described as meeting the required performance. The abstract frames sharper and deeper wide-field data than JWST as a promise of ELTs equipped with multi-conjugate adaptive optics, not an observed result; it reports an instrument concept rather than astronomical findings or demonstrated on-sky performance.

PublicSHARP is a proposed instrument for ESO’s upcoming Extremely Large Telescope. It would separate near-infrared light into spectra to help researchers study questions about both the nearby and distant Universe. Its design combines NEXUS, intended to study many very faint sources, with VESPER, intended to collect spatially resolved spectra of multiple brighter sources. The presentation explains the scientific goals and the optical design developed to meet them. The prospect of images sharper and deeper than those from the James Webb Space Telescope is a motivation for these large, atmosphere-corrected telescopes, not a demonstrated result from SHARP.

Young explorerScientists are planning a new tool called SHARP for a giant telescope that is coming in the future. It would spread out invisible light into different colors to help them learn about things near and far away in space. One part would look at very faint things, and another would study brighter things in more detail. This is a plan for a tool, not a report of things it has already discovered.

Object-independent evaluation of small-data astronomical image classifiers: architecture, representation, and acquisition shortcuts

Eraldo Pereira Marinho

• Computer Vision and Pattern Recognition

AstronomerThis study tests how morphology, image context, acquisition settings, and catalogue-derived properties contribute to four-class astronomical image classification. The dataset comprises 370 catalogue-supported physical objects—galaxies, globular clusters, nebulae, and open clusters—with three Digitised Sky Survey FITS bands per object and an object-group-constrained 222/75/73 training/validation/test split. Across three fixed seeds, adaptive full-field test balanced accuracies were 0.773±0.014 for a CNN–Transformer trained from scratch, 0.874±0.054 for ImageNet-pretrained ResNet-50, and 0.866±0.023 for ImageNet-pretrained ViT-B/16. No primary architecture contrast rejected its null after Holm correction; the ResNet-50–ViT-B/16 difference was 0.007, with a 95% cluster-bootstrap interval of [-0.048, 0.062]. Comparisons included a common angular field and two central-region-masked controls. Acquisition/catalogue metadata controls achieved 0.721–0.735, while masked adaptive views achieved 0.731–0.800. The tests demonstrate generalisation to unseen physical objects within this dataset, but substantial class information remains outside target morphology. High accuracy therefore does not establish morphology learning, and the design does not separate architecture effects from pretraining.

PublicResearchers tested whether image-classifying AI recognises astronomical objects by their appearance or also relies on other clues. They used images of 370 galaxies, globular clusters, nebulae, and open clusters, keeping different physical objects in the training and test sets. Two models previously trained on ImageNet had higher average scores than a model trained from scratch, but the statistical tests did not establish differences among the models. Crucially, information about image acquisition and catalogue properties could also predict the object classes, and classifiers still performed substantially above chance when central image regions were hidden. The models could classify objects they had not encountered during training, but that success does not prove they learned the objects’ shapes. The comparison also cannot disentangle model design from the benefit of prior training.

Young explorerScientists taught computers to sort sky pictures into four kinds of objects. Then they tested them on objects the computers had not practised with. The computers could sort many pictures, but there was a catch: they could also use clues besides the objects’ shapes. Even hiding the middle of the pictures left useful clues. So getting an answer right does not prove a computer learned to recognise the object’s shape.

Adaptive Optics for the Extremely Large Telescope: overcoming Point Spread Function challenges with MORFEO

Carmelo Arcidiacono, Elisa Portaluri, Marco Gullieuszik+6 more

AstronomerThe paper reviews MORFEO, the ELT’s multi-conjugate adaptive-optics relay, and its relevance to wide-field spectroscopy. Its architecture combines telescope mirrors M4–M5 with two post-focal deformable mirrors to provide a stable, diffraction-limited PSF over a field approaching 1 arcminute. Atmospheric sensing uses six sodium laser guide stars and up to three natural guide stars across an approximately 160-arcsecond technical field, with quoted sky coverage of order 50% at the South Galactic Pole. Two gravity-invariant ports serve MICADO, with a 51-arcsecond corrected field, and HARMONI. The review addresses optical quality, atmospheric tomography, corrected-focal-plane stability, and telemetry-based PSF reconstruction. SHARP remains a multi-object near-infrared spectrograph concept that uses MORFEO as its reference MCAO architecture for performance evaluation. The abstract describes capabilities and design relevance but supplies no quantitative validation of the reviewed performance metrics.

PublicMORFEO is a system for the Extremely Large Telescope that uses adjustable mirrors to counteract atmospheric blurring across a patch of sky. Six laser guide stars and up to three real stars help it sense the atmosphere. The paper reviews how well this approach can maintain sharp, stable images and support the MICADO and HARMONI instruments. It also discusses its relevance to SHARP, a proposed instrument for studying the near-infrared light of multiple objects at once. SHARP uses MORFEO as a reference design for evaluating performance; the abstract does not report demonstrated SHARP results.

Young explorerEarth’s air can make a telescope’s pictures look blurry. MORFEO uses mirrors that change shape, with help from laser-made guide stars and real stars, to make pictures sharper. This paper explains the system and how it could help another instrument that scientists are still planning.

Tracking turbulence for wind-driven halo removal using MagAO-X pyramid wavefront sensor images

Jay K. Kueny, Jared R. Males, Alycia J. Weinberger+16 more

AstronomerUsing archival MagAO-X wavefront-sensor telemetry, the authors demonstrate reconstruction and removal of the wind-driven halo in individual coronagraphic science images. This low-spatial-frequency artifact arises from adaptive-optics servo lag and varies in intensity and position angle, making subtraction difficult without compromising extended emission. Their windsoCC pipeline cross-correlates recorded closed-loop residual wavefronts to measure wind vectors for several turbulent atmospheric layers above Las Campanas Observatory. These inferred wind parameters feed a parametric model of the halo footprint. Applied to on-sky visible-light MagAO-X images of the HR 4796A disk, the workflow demonstrates what the authors describe as a dramatic improvement in object recovery; the abstract gives no quantitative recovery metrics.

PublicAdaptive optics corrects atmospheric blurring, but delays in those corrections leave a changing pattern of unwanted light called the wind-driven halo. Removing this pattern can also erase light from extended objects such as disks around stars. The researchers used archived measurements from the MagAO-X instrument’s wavefront sensor to work out wind motions in several turbulent atmospheric layers. They then used those wind estimates in a model to reconstruct and remove the unwanted pattern from individual images. In real visible-light observations of the disk around HR 4796A, they report a dramatic improvement in recovering the disk’s light, although the abstract does not quantify the improvement.

Young explorerMoving air makes telescope pictures blurry. A telescope tool helps fix that, but it is a little late and leaves an unwanted glow. Taking away the glow can accidentally take away part of the thing we want to see. The researchers used the tool’s saved records to figure out how the air was moving, then made a model to help remove the glow. They tried it on real pictures of a disk around a star and say the disk became much easier to see.

Near-Quantum-Limited Readout for the Princeton Axion Search using a sub-GHz Kinetic Inductance Traveling Wave Parametric Amplifier

Joe Wiedemann, Roman Kolevatov, Jianyang Fu+7 more

• Quantum Physics
• High Energy Physics - Experiment

AstronomerThe authors report a kinetic inductance traveling-wave parametric amplifier (KI-TWPA) operating at 300–700 MHz, with gain exceeding 30 dB and pump powers of a few hundred nanowatts. A variable-temperature noise source yields a measured system noise of 2.5–3.5 quanta. For potential axion-search applications, they characterize gain drift, compression point, amplifier noise at different operating temperatures, readout with an input circulator, and magnetic-field insensitivity. The device extends parametric-amplifier development into the comparatively less developed sub-GHz regime; applications to axion searches, semiconductor spin-qubit readout, and superconducting detector arrays are prospective, not demonstrations reported in this abstract.

PublicResearchers report a low-noise amplifier that strengthens signals at frequencies of 300–700 MHz, a range where this kind of amplifier has been less developed. It provides more than 30 decibels of gain while using a pump power of a few hundred nanowatts. Tests measured system noise of 2.5–3.5 quanta, a measure of noise on the quantum scale. The team also studied performance factors relevant to searches for hypothetical axion particles, including stability, signal-handling limits, temperature effects, and sensitivity to magnetic fields. The amplifier could support those searches, quantum-computer readout, and detector arrays, but the abstract does not report an axion detection or demonstrations of those applications.

Young explorerScientists made a new device that makes faint signals stronger, a little like turning up a very quiet sound. They tested how much it boosts signals and how much extra fuzziness comes along with them. They also checked things like whether its boosting stays steady. One day, it could help scientists look for tiny particles called axions, but this work did not find any axions.

Hard X-ray/Soft gamma-ray Laue Lenses for High Energy Astrophysics

Filippo Frontera

• High Energy Physics - Experiment
• Medical Physics

AstronomerThis review addresses the astrophysical importance and instrumental challenges of hard X-ray/soft gamma-ray astronomy in the 20 keV–1 MeV band, particularly the difficulty of achieving the required sensitivity with current instrumentation. It discusses focusing Laue lenses as a possible solution, covering operating principles, approaches to high reflection efficiency, imaging properties, feasibility studies, technological developments, and observational prospects. The abstract presents an instrumentation review and a proposed approach, not new astronomical measurements or a demonstrated sensitivity improvement.

PublicStudying the sky with hard X-rays and soft gamma rays is scientifically valuable, but current instruments struggle to reach the sensitivity needed. This review explores a possible way forward: focusing radiation with a device called a Laue lens. It discusses how such lenses work, how efficiently they could reflect radiation, their imaging capabilities, and progress toward making them practical. The abstract does not report a working solution or new observations.

Young explorerScientists want to study a kind of light from space that is hard to detect. This review talks about a special lens that might help them see it better. It explains the idea and the work toward making it useful, but does not say the problem is solved.

SHARP -- A spectrograph proposal to fully exploit ELT capabilities and look beyond JWST

P. Saracco, P. Conconi, C. Arcidiacono+47 more

AstronomerSHARP is a concept study for a 0.95–2.45 μm spectrograph intended to exploit the collecting area and angular resolution of ESO’s upcoming ELT. Its science drivers span primordial galaxies and the formation of young stellar objects and planetary systems in nearby dust-obscured regions. The proposed architecture combines NEXUS, a multi-object spectrograph optimized for the faintest sources, with VESPER, a multi-object integral-field unit intended for brighter sources. The article presents the science requirements, design solutions, and resulting optical design, reported to meet the required performance. The prospect of sharper and deeper wide-field data than JWST is presented as a promise of ELTs with multi-conjugate adaptive optics, not an observational result.

PublicSHARP is a proposed infrared instrument for ESO’s upcoming Extremely Large Telescope. It is designed to help astronomers investigate both the earliest galaxies and the formation of stars and planetary systems in nearby dusty regions. One component, NEXUS, would study very faint targets, while another, VESPER, would collect spatially resolved spectra of brighter targets. The article describes the scientific goals and optical design rather than reporting new astronomical observations. The expected ability of extremely large telescopes to deliver sharper images and detect fainter sources than JWST across large fields remains a promise, not a demonstrated result here.

Young explorerAstronomers are planning a tool called SHARP for a huge new telescope. It would spread light into different colors to help them learn about faraway galaxies and places hidden in dust where stars and planets are forming. One part would look at very faint things, and another would look at brighter things. This paper tells us about the plan, not discoveries made with the tool.

Fast Graph-based Higher-Order Clustering Statistics on the GPU

Cristiano G. Sabiu

• Cosmology and Nongalactic Astrophysics

AstronomerGRAMSCI v2 updates graph-based estimation of general N-point spatial correlation functions. A merge-walk replaces the binary-search inner loop, reducing its per-hub–spoke cost from O(m log m) to O(m), where m is the mean neighbor count. New features include even/odd parity decomposition of the 4pCF, internal estimation of the disconnected contribution to obtain the connected 4pCF, and a Python/NumPy interface to the Fortran engine. An OpenACC GPU port delivers measured speedups of 2.6× for the 3pCF to 9× for the 4pCF on a single consumer GPU relative to a 64-thread CPU node. Out-of-core tiling enables a BAO-scale 3pCF calculation on a graph with 9 billion edges using a 24 GB GPU, with approximately 20% overhead. Validation includes CPU-reference comparisons, analytic injection tests, and exactly solvable non-Gaussian and Gaussian random fields, whose full and connected 4pCFs are recovered without bias in these tests. Applications to DESI DR1 LRG data demonstrate the 3pCF and full and connected 4pCF across the complete configuration space out to 150 h⁻¹ Mpc.

PublicThe researchers present a faster version of GRAMSCI, software that measures how points, such as galaxies, cluster in groups of three, four, or more. The update improves the calculation method, adds ways to separate different contributions to four-point patterns, and lets the main calculations run on a graphics processor. In their benchmarks, one consumer graphics processor was 2.6 to 9 times faster than a 64-thread CPU computer, depending on the calculation. The software can also process graphs too large to fit in the graphics processor’s memory at once. The team checked it against reference calculations and mathematical test patterns, then demonstrated it on galaxy data from DESI. These are software-performance and validation results, alongside applications to real data, rather than a claim of a new cosmological discovery.

Young explorerGalaxies make patterns in space. Scientists improved a computer tool that looks for patterns made by three or four dots at a time. They made it run faster using a graphics chip. They checked it with made-up patterns whose answers were known, and also used it on a real galaxy map.

MACE: Multigroup-Multiangle Integrated Thermal Compton Scattering Kernel

Itamar Giron, Menahem Krief, Elad Steinberg

• High Energy Astrophysical Phenomena

AstronomerThe authors present Compton-scattering tables for multigroup, multiangle radiation transport, integrating the exact thermal Compton kernel over incident-energy groups, scattered-energy groups, and angular bins. Their deterministic method combines robust pointwise kernel evaluation with nested quadratures whose panels adapt to the recoil ridge, thermal broadening, and nearly elastic forward-scattering boundary layer. They validate the tables against published kernel profiles, angular and energy moments, mean free paths, multigroup redistribution data, and an independent Monte Carlo estimator. The output consists of redistribution matrices and angular moments for transport calculations; this is a numerical-method and data-resource result, not an astronomical observation.

PublicThe researchers have produced numerical tables to help calculate how Compton scattering changes radiation’s energy and direction. Their method carefully handles features of the scattering calculation that are difficult to integrate accurately. They checked the tables against published calculations and a separate calculation based on random sampling. The resulting tables are intended to make radiation-transport calculations accurate, reproducible, and easier to carry out. The work provides a computational resource rather than reporting observations of an astronomical object.

Young explorerLight can change its energy and direction when it scatters. The researchers made careful number tables to help computers work out those changes. They checked their tables against other calculations to see whether they agreed. These tables are tools for studying how light travels, not pictures or measurements of something in space.